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Geographic Information and Concentrations (Tables)

12 Months Ended

Dec. 31, 2019

Geographic Information and Concentrations

Revenue by geographic areas for the years ended December 31, 2019, 2018 and 2017, are as follows (in thousands):


	Year Ended December 31,
	2019		2018		2017
United States	$	—	$	—	$	—
International:
North America (1)		—		2,320		—
Asia Pacific (2) (3) (4)		5,281		287		42,000
Total revenue	$	5,281	$	2,607	$	42,000

(1)Revenues from North America in 2018 comprised of $2.3 million from Canada in accordance with the Knight Agreement.

(2)Revenues from Asia Pacific in 2019 comprised $0.3 million and $0.5 million from Japan in accordance with the 2017 KKC Agreement and 2019 KKC Agreement, respectively, $1.5 million from Hong Kong in accordance with the XuanZhu Agreement and $3.0 million from China in accordance with the Fosun Agreement.

(3) Revenues from Asia Pacific in 2018 comprised $0.3 million from Japan in accordance with the 2017 KKC Agreement.

(4) Revenues from Asia Pacific in 2017 included $30.0 million from Japan in accordance with the 2017 KKC Agreement and $12.0 million from China in accordance with the Fosun Agreement.

Schedule of Collaboration Partnerships


	Year Ended December 31,
	2019		2018		2017
Fosun Pharma	57	%	—		29	%
XuanZhu	28	%	—		—
KKC	15	%	11	%	71	%
Knight	—		89	%	—

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 181,133	$ 78,768
Short-term investments	66,379	89,321
Accounts receivable		85
Unbilled revenue	750	5,000
Prepaid expenses and other current assets	3,800	3,197
Total current assets	252,062	176,371
Property and equipment, net	3,436	5,611
Right-of-use assets	3,970
Other assets	314	1,350
Total assets	259,782	183,332
Current liabilities:
Accounts payable	2,187	1,148
Accrued compensation and benefits	4,453	2,723
Uncharged license fees		1,000
Current portion of operating lease liability	2,608
Loan payable, current portion	1,183
Deferred revenue	4,541
Accrued expenses and other current liabilities	7,248	12,857
Total current liabilities	22,220	17,728
Operating lease liability, net of current portion	2,076
Loan payable, net of current portion	48,831	49,209
Other long-term liabilities		582
Total liabilities	73,127	67,519
Commitments and contingencies (Note 17)
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; no shares issued and outstanding as of December 31, 2019 and December 31, 2018, respectively.
Common stock, $0.0001 par value; 300,000,000 shares authorized; 88,817,741 and 62,516,627 shares issued and outstanding as of December 31, 2019 and December 31, 2018, respectively.	9	6
Additional paid-in capital	647,078	481,357
Accumulated deficit	(460,452)	(365,512)
Accumulated other comprehensive income (loss)	20	(38)
Total stockholders' equity	186,655	115,813
Total liabilities and stockholders' equity	$ 259,782	$ 183,332

Statements of Stockholders' Equity - USD ($)	Common Stock [Member] Public Offering [Member]	Common Stock [Member] Private Investment in Public Equity (PIPE) [Member]	Common Stock [Member] Underwriters' Option	Common Stock [Member] Restricted Stock Units (RSUs) [Member]	Common Stock [Member]	Additional Paid-In Capital [Member] Public Offering [Member]	Additional Paid-In Capital [Member] Private Investment in Public Equity (PIPE) [Member]	Additional Paid-In Capital [Member] Underwriters' Option	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Other Comprehensive Income (Loss) [Member] Restricted Stock Units (RSUs) [Member]	Other Comprehensive Income (Loss) [Member]	Public Offering [Member]	Private Investment in Public Equity (PIPE) [Member]	Underwriters' Option	Restricted Stock Units (RSUs) [Member]	Total
Balance, amount at Dec. 31, 2016					$ 5,000				$ 407,092,000	$ (213,875,000)		$ (71,000)					$ 193,151,000
Balance, shares at Dec. 31, 2016					47,309,422
Issuance of common stock under employee stock purchase plan, amount									62,000								$ 62,000
Issuance of common stock under employee stock purchase plan, shares					35,759
Issuance of common stock for services, shares					43,597												46,858
Issuance of common stock upon exercise of options									9,590,000								$ 9,590,000
Stock-based compensation										(64,339,000)							(64,339,000)
Other comprehensive loss																	24,000
Issuance of common stock, value						$ 201,000	$ 623,000				$ 24,000		$ 201,000	$ 623,000		$ 24,000
Issuance of common stock, shares	46,858	99,343
Net loss																	(64,339,000)
Balance, amount at Dec. 31, 2017					$ 5,000				417,568,000	(278,214,000)		(47,000)					139,312,000
Balance, shares at Dec. 31, 2017					47,534,979
Issuance of common stock under employee stock purchase plan, amount									491,000								491,000
Issuance of common stock under employee stock purchase plan, shares					120,959
Issuance of common stock for services, amount									303,000								$ 303,000
Issuance of common stock for services, shares					75,183												75,183
Issuance of common stock upon exercise of options									9,226,000								$ 9,226,000
Issuance of common stock upon exercise of options, shares					14,375,000
Stock-based compensation					$ 1,000				53,769,000								53,770,000
Other comprehensive loss																	9,000
Issuance of common stock, value											$ 9,000					$ 9,000
Issuance of common stock, shares				410,506
Net loss										(91,298,000)							(91,298,000)
Balance, amount at Dec. 31, 2018					$ 6,000				481,357,000	(365,512,000)		(38,000)					115,813,000
Balance, shares at Dec. 31, 2018					62,516,627
Adoption of ASU No. 2014-09 on January 1, 2018										4,000,000							4,000,000
Issuance of common stock under employee stock purchase plan, amount									396,000								396,000
Issuance of common stock under employee stock purchase plan, shares					160,744
Issuance of common stock for services, amount									312,000								$ 312,000
Issuance of common stock for services, shares					113,136												113,136
Issuance of common stock upon exercise of options									178,000								$ 178,000
Issuance of common stock upon exercise of options, shares					68,062												68,062
Stock-based compensation									9,936,000								$ 9,936,000
Other comprehensive loss												58,000					58,000
Issuance of common stock, value			$ 3,000					$ 134,924,000							$ 134,927,000
Issuance of common stock, shares			23,000,000	85,609
Net loss										(94,940,000)							(94,940,000)
Balance, amount at Dec. 31, 2019					$ 9,000				647,078,000	$ (460,452,000)		$ 20,000					186,655,000
Balance, shares at Dec. 31, 2019					88,817,741
Adoption of ASU No. 2014-09 on January 1, 2018 \| ASU 2014-09					$ 2,873,563				$ 19,975,000								$ 19,975,000

Fair Value Measurements - Changes in Fair Value of Recurring Measurements (Details) - Derivative Liability Exit Fee [Member] - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		$ 533
Change in estimated fair value of derivative liability for exit fee	$ 546	436	$ (13)
Ending Balance		$ 969	$ 533

Income Taxes - Significant Components of the Company's Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets, Net [Abstract]
Amortization and depreciation	$ 45,555	$ 38,376
Net operating loss carryforwards	40,896	31,621
Tax credits	10,136	8,200
Stock-based compensation	4,853	3,763
Lease obligation	984	0
Other	940	888
Gross deferred tax assets	103,364	82,848
Valuation allowance	(102,344)	(81,645)
Deferred tax assets net of valuation allowance	1,020	1,203
Deferred Tax Liabilities, Net [Abstract]
Right of use asset	(834)	0
Revenue recognition	(158)	(1,054)
Other	(28)	(149)
Net deferred tax assets	$ 0	$ 0

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation

The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

Prior Period Errors

In connection with our review of our financial statements as of and for the six months ended June 30, 2019, we corrected errors related to the accounting for clinical trial accruals that had resulted in an overstatement of research and development expenses during the year ended December 31, 2018. Specifically, management concluded that the Company’s research and development expenses recorded during the year ended December 31, 2018 had been overstated by $3.6 million and that the Company’s accrued expenses and other current liabilities as of December 31, 2018 had been overstated by the same amount.

Management analyzed the potential impact of these errors in accordance with the U.S. Securities and Exchange Commission’s (“SEC”) Staff Accounting Bulletin No. 108, Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements, and concluded that while the errors were significant to the Company’s financial statements as of and for the six months ended June 30, 2019, a correction of the errors would not have been material to the full year results for 2019 and 2018 nor affect the trend of financial results. Accordingly, the Company reduced accrued and other liabilities by $3.6 million and recorded a cumulative adjustment of $3.6 million in the statement of operations and comprehensive loss to reduce research and development expenses in 2019.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to recognition of revenue, clinical trial accruals, contract manufacturing accruals, fair value of assets and liabilities, income taxes and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could materially differ from those estimates.

Liquidity

As of December 31, 2019, the Company had cash and cash equivalents and short-term investments of approximately $247.5 million, which include net proceeds of approximately $134.9 million and approximately $20.0 million received in connection with the 2019 Offering and the Private Placement, respectively, as defined and discussed in Note 7. We believe our current available cash, cash equivalents and short-term investments will be sufficient to fund our planned expenditures and meet the Company’s obligations for at least 12 months following March 6, 2020, which is the date that the financial statements are being issued.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with an original maturity date of 90 days or less on the date of purchase to be cash equivalents.

Short-Term Investments

Short-term investments consist of debt securities classified as available-for-sale and have maturities greater than 90 days, but less than one year, from the date of acquisition. Short-term investments are carried at fair value based upon quoted market prices. Unrealized gains and losses on available-for-sale securities are excluded from earnings and are reported as a component of accumulated other comprehensive loss. The cost of available-for-sale securities sold is based on the specific-identification method.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, short-term investments and accounts receivable. The Company is exposed to credit risks in the event of default by the counterparties to the extent of the amount recorded in its balance sheet. Cash, cash equivalents and short-term investments are invested through banks and other financial institutions in the United States.

Accounts Receivable

An allowance for doubtful accounts will be recorded based on a combination of historical experience, aging analysis, and information on specific accounts. Account balances will be written off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote. No provision was made for doubtful accounts as of December 31, 2019, 2018 and 2017.

Foreign Currency and Forward Contracts

The Company manages its foreign currency exposures with the use of foreign currency purchases as well as currency spot and forward contracts. The Company primarily conducts its business in U.S. dollars; however, a portion of the Company’s expense and capital activities are transacted in foreign currencies which are subject to exchange rate fluctuations that can affect cash or earnings. The Company has been in a loss position and therefore its primary objective is to conserve and manage cash. There are generally two methods by which the Company manages the cash flow risk of foreign exchange fluctuations when a contract is signed (i) it can purchase the foreign funds, in full or in part, upon the execution of the contract, or (ii) it can obtain the right to purchase such funds, in full or in part, at the execution of the contract, i.e., obtain a forward contract from an appropriate bank, that can be exercised to obtain the currency of interest at a particular point in time. The derivative instruments that the Company uses to hedge the exposure shall generally not be designated as cash flow hedges, and as a result, changes in their fair value will be recorded in other income (expense), net, in the Company's statements of operations and comprehensive loss. The fair values of forward foreign currency exchange contracts are estimated using current exchange rates and interest rates and the current creditworthiness of the counterparties is taken into consideration.

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, with ranges generally from three to five years. Leasehold improvements are amortized over the lesser of the estimated useful lives or the related remaining lease term.

Impairment of Long-Lived Assets

The carrying value of long-lived assets, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the asset may not be recoverable. An impairment loss is recognized when the total of estimated future undiscounted cash flows, expected to result from the use of the asset and its eventual disposition, are less than the asset’s carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. For the years ending December 31, 2019, 2018 and 2017 there have been no impairment losses.

Income Taxes

The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized.

Revenue Recognition

On January 1, 2018 the Company adopted the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) and related amendments (“ASC 606”), on a modified retrospective basis, which resulted in an adjustment to the opening accumulated deficit balance on the adoption date. As a result of the adoption of the new standard, on January 1, 2018, the Company recorded the following: (i) unbilled revenue under current assets of $5.0 million representing a future receivable related to the first milestone under the Company’s license agreement with Kyowa Kirin Co., Ltd. (formerly known as Kyowa Hakko Kirin Co., Ltd, or KHK) (“KKC”), which was subsequently achieved by KKC and collected in February 2019, thereby reducing the unbilled revenue balance to zero, (ii) uncharged license fees under current liabilities of $1.0 million representing the corresponding future payable related to AstraZeneca AB, or AstraZeneca, in accordance with the Company’s termination agreement with AstraZeneca, which, upon KKC achieving the milestone, was reclassified to accounts payable and subsequently paid to AstraZeneca during the second quarter of 2019, and (iii) a related decrease in accumulated deficit of approximately $4.0 million as the new standard permitted revenue from milestones that possess certain criteria to be recognized earlier and also contained different recognition criteria related to milestones than under the previous accounting standard.

The Company generates revenue primarily from research and collaboration and license agreements with customers. Goods and services in the agreements may include the grant of licenses for the use of the Company’s technology, the provision of services associated with the research and development of product candidates, manufacturing services, and participation in joint steering committees. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, up-front license fees; research, development, regulatory and commercial milestone payments; reimbursement of research and development services; option payments; reimbursement of certain costs; payments for manufacturing supply services; and future royalties on net sales of licensed products.

When two or more contracts are entered into with the same customer at or near the same time, the Company evaluates the contracts to determine whether the contracts should be accounted for as a single arrangement. Contracts are combined and accounted for as a single arrangement if one or more of the following criteria are met: (i) the contracts are negotiated as a package with a single commercial objective; (ii) the amount of consideration to be paid in one contract depends on the price or performance of the other contract; or (iii) the goods or services promised in the contracts (or some goods or services promised in each of the contracts) are a single performance obligation.

In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, management performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraints on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for contracts with customers, the Company develops assumptions that require judgment to determine whether promised goods and services represent distinct performance obligations and the standalone selling price for each performance obligation identified in the contract. This evaluation is subjective and requires the Company to make judgments about the promised goods and services and whether those goods and services are separable from other aspects of the contract. Further, determining the standalone selling price for performance obligations requires significant judgment, and when an observable price of a promised good or service is not readily available, the Company considers relevant assumptions to estimate the standalone selling price, including, as applicable, market conditions, development timelines, probabilities of technical and regulatory success, reimbursement rates for personnel costs, forecasted revenues, potential limitations to the selling price of the product and discount rates.

The Company applies judgment in determining whether a combined performance obligation is satisfied at a point in time or over time, and, if over time, concluding upon the appropriate method of measuring progress to be applied for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, as estimates related to the measure of progress change, related revenue recognition is adjusted accordingly. Changes in the Company’s estimated measure of progress are accounted for prospectively as a change in accounting estimate. The Company recognizes collaboration revenue by measuring the progress toward complete satisfaction of the performance obligation using an input measure. In order to recognize revenue over the research and development period, the Company measures actual costs incurred to date compared to the overall total expected costs to satisfy the performance obligation. Revenues are recognized as the program costs are incurred. The Company will re-evaluate the estimate of expected costs to satisfy the performance obligation each reporting period and make adjustments for any significant changes.

Amounts received prior to satisfying the revenue recognition criteria are recorded as contract liabilities in the Company’s balance sheets. If the related performance obligation is expected to be satisfied within the next twelve months this will be classified in current liabilities. Amounts recognized as revenue prior to receipt are recorded as contract assets in the Company's balance sheets. If the Company expects to have an unconditional right to receive the consideration in the next twelve months, this will be classified in current assets. A net contract asset or liability is presented for each contract with a customer.

Milestone Payments: At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur and when the uncertainty associated with the variable consideration is subsequently resolved. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative standalone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraints, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect earnings in the period of adjustment.

Manufacturing supply services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are generally considered as options. The Company assess if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations. If the Company is entitled to additional payments when the customer exercises these options, any payments are recorded in other revenues when the customer obtains control of the goods, which is upon delivery.

Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and where the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

Licenses of intellectual property: If a license granted to a customer to use the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from consideration allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company applies judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, to conclude upon the appropriate method of measuring progress for purposes of recognizing revenue related to consideration allocated to the performance obligation.

Options: Customer options, such as options granted to allow a licensee to choose to research, develop and commercialize licensed compounds are evaluated at contract inception in order to determine whether those options provide a material right (i.e., an optional good or service offered for free or at a discount) to the customer. If the customer options represent a material right, the material right is treated as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the standalone selling price, and revenue is recognized when or as the future goods or services are transferred or when the option expires. Customer options that are not material rights do not give rise to a separate performance obligation, and as such, the additional consideration that would result from a customer exercising an option in the future is not included in the transaction price for the current contract. Instead, the option is deemed a marketing offer, and additional option fee payments are recognized or being recognized as revenue when the licensee exercises the option. The exercise of an option that does not represent a material right is treated as a separate contract for accounting purposes.

Contract costs: The Company recognizes as an asset the incremental costs of obtaining a contract with a customer if the costs are expected to be recovered. The Company has elected a practical expedient wherein it recognizes the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that it otherwise would have recognized is one year or less. To date, the Company has not incurred any material incremental costs of obtaining a contract with a customer.

Contract modifications: Contract modifications, defined as changes in the scope or price (or both) of a contract that are approved by the parties to the contract, such as a contract amendment, exist when the parties to a contract approve a modification that either creates new or changes existing enforceable rights and obligations of the parties to the contract. Depending on facts and circumstances, the Company accounts for a contract modification as one of the following: (i) a separate contract; (ii) a termination of the existing contract and a creation of a new contract; or (iii) a combination of the preceding treatments. A contract modification is accounted for as a separate contract if the scope of the contract increases because of the addition of promised goods or services that are distinct and the price of the contract increases by an amount of consideration that reflects the Company’s standalone selling prices of the additional promised goods or services. When a contract modification is not considered a separate contract and the remaining goods or services are distinct from the goods or services transferred on or before the date of the contract modification, the Company accounts for the contract modification as a termination of the existing contract and a creation of a new contract. When a contract modification is not considered a separate contract and the remaining goods or services are not distinct, the Company accounts for the contract modification as an add-on to the existing contract and as an adjustment to revenue on a cumulative catch-up basis.

The Company receives payments from its licensees as established in each contract. Upfront payments and fees are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Where applicable, amounts are recorded as unbilled revenue when the Company’s right to consideration is unconditional. The Company does not assess whether a contract with a customer has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less.

Research and Development Costs

Research and development costs are charged to expense as incurred and consist of costs incurred to further the Company’s research and development activities and include salaries and related employee benefits, costs associated with clinical trials, costs related to pre-commercialization manufacturing activities such as manufacturing process validation activities and the manufacturing of clinical drug supply, nonclinical research and development activities, regulatory activities, research-related overhead expenses and fees paid to external service providers and contract research and manufacturing organizations that conduct certain research and development activities on behalf of the Company.

Accrued Research and Development Expenses

The Company is required to estimate its accrued expenses at the end of each reporting period. This process involves reviewing open contracts and purchase orders, communicating with Company personnel to identify services that have been performed on the Company’s behalf and estimating the level of service performed and the associated cost incurred for the service when the Company has not yet been invoiced or otherwise notified of the actual costs. The majority of the Company’s service providers submit invoices in arrears for services performed or when contractual milestones are met. The Company makes estimates of its accrued expenses as of each balance sheet date in the financial statements based on facts and circumstances known to the Company at that time. The Company periodically confirms the accuracy of its estimates with the service providers and makes adjustments if necessary. Examples of estimated accrued research and development expenses include fees paid to:

contract research organizations, or CROs, in connection with clinical studies;

investigative sites in connection with clinical studies;

vendors related to product manufacturing, development and distribution of clinical supplies; and

vendors in connection with preclinical development activities.

The Company records expenses related to clinical studies and manufacturing development activities based on its estimates of the services received and efforts expended pursuant to contracts with multiple CROs and manufacturing vendors that conduct and manage these activities on the Company’s behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract, and may result in uneven payment flows. There may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense. Payments under some of these contracts depend on factors such as the successful enrollment of subjects and the completion of clinical trial milestones. In accruing service fees, the Company estimates the time period over which services will be performed, enrollment of subjects, number of sites activated and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the Company’s estimate, the Company will adjust the accrued or prepaid expense balance accordingly.

Stock-Based Compensation

The Company recognizes compensation expense for all stock-based payment awards made to employees, nonemployees and directors based on estimated fair values. For employee and nonemployee stock options, the Company determines the grant date fair value of the awards using the Black-Scholes option-pricing model and generally recognizes the fair value as stock-based compensation expense on a straight-line basis over the vesting period of the respective awards. For restricted stock and performance-based restricted stock, to the extent they are probable, the compensation cost for these awards is based on the closing price of the Company’s common stock on the date of grant and recognized as compensation expense on a straight-line basis over the requisite service period. Stock-based compensation expense is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.

Derivatives and Hedging Activities

The Company accounts for its derivative instruments as either assets or liabilities on the balance sheet and measures them at fair value. Derivatives are adjusted to fair value through other income (expense), net in the statements of operations and comprehensive loss.

Leases

The Company determines if an arrangement is a lease at the inception of the arrangement. Operating leases are included in right-of-use assets, current portion of operating lease liability, and operating lease liability, net of current portion in our balance sheets. Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The operating lease right-of-use assets also include any lease payments made and exclude lease incentives. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise any such options. Lease expense is recognized on a straight-line basis over the expected lease term. The Company has elected not to separate lease and non-lease components, such as common area maintenance charges, and instead it accounts for these as a single lease component.

Comprehensive Loss

Comprehensive loss is composed of two components: net loss and other comprehensive income (loss). Other comprehensive income (loss) refers to gains and losses that are recorded as an element of stockholders’ equity but are excluded from net loss.

Net Loss per Share

Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration of potential common shares. Diluted net loss per common share in the periods presented is the same as basic net loss per common share, since the effects of potentially dilutive securities are antidilutive due to the net loss for all periods presented.

Recent Accounting Pronouncements

New Accounting Pronouncements - Recently Adopted

On January 1, 2019, the Company adopted the FASB’s Accounting Standards Update (“ASU”), No. 2018-07, Compensation – Stock Compensation, which simplifies the accounting for share-based payments to non-employees by aligning it with the accounting guidance for share-based payments for employees. This ASU expands the scope of Topic 718, Compensation – Stock Compensation, which currently only includes share-based payments issued to employees, to also include share-based payments issued to non-employees for goods and services. Consequently, the accounting for share-based payments to non-employees and employees is substantially aligned. The adoption of this standard did not have a material impact on the Company’s financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), as amended, which generally requires lessees to recognize operating and financing lease liabilities and corresponding right-of-use assets on the balance sheet and to provide enhanced disclosures surrounding the amount, timing and uncertainty of cash flows arising from leasing arrangements. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”). In issuing ASU 2018-11, the FASB permitted another transition method for ASU 2016-02, which allows the transition to the new lease standard by recognizing a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The Company elected the transition method and package of practical expedients permitted under the transition guidance, which allowed the Company to carryforward its historical lease classification, its assessment on whether a contract is or contains a lease, and its initial direct costs for any leases that exist prior to adoption of the new standard. The Company also elected to combine lease and non-lease components and to keep leases with an initial term of 12 months or less off the balance sheet and recognize the associated lease payments in the statements of operations on a straight-line basis over the lease term. We adopted the ASU on January 1, 2019 using a modified retrospective approach and recorded a right-of-use asset and a corresponding lease liability to account for our facility lease as a cumulative-effect adjustment to the opening balance of accrued expense and other current liabilities and other long-term liabilities in the period of adoption.

Impact of Adoption

The Company, on adopting Topic 842 on January 1, 2019, used the modified retrospective approach with the cumulative effect of initially applying the standard as an adjustment to the opening balance of accrued and other liabilities and other long-term liabilities. The following adjustments were recorded in the Company’s balance sheet on January 1, 2019 (in thousands):


	December 31,		Adjustments		January 1,
	2018		Due to Topic 842		2019
Right-of-use assets	$	—	$	5,810	$	5,810
Current portion of operating lease liability	$	—	$	1,892	$	1,892
Operating lease liability, net of current portion	$	—	$	4,684	$	4,684
Accrued expenses and other current liabilities	$	12,857	$	(184)	$	12,673
Other long-term liabilities	$	582	$	(582)	$	—

As a result of adopting Topic 842 on January 1, 2019, the following financial statement line items in the Company’s balance sheet at December 31, 2019 and the statement of operations and comprehensive loss for the year ended December 31, 2019 were affected compared to as would have been recorded under ASC 840, Leases (Topic 840), (in thousands):


	December 31, 2019
	As Reported under Topic 842		Under Topic 840		Effect of Change
Right-of-use assets	$	3,970	$	—	$	3,970
Current portion of operating lease liability	$	2,608	$	—	$	2,608
Operating lease liability, net of current portion	$	2,076	$	—	$	2,076
Accrued expenses and other current liabilities	$	7,248	$	7,571	$	(323)
Other long-term liabilities	$	—	$	258	$	(258)


	Year Ended December 31, 2019
	As Reported under Topic 842		Under Topic 840		Effect of Change
Operating expenses:
Research and development related to leases	$	2,070	$	1,962	$	108
General and administrative related to leases		522		498		24
Total	$	2,592	$	2,460	$	132

New Accounting Pronouncements – Adoption on January 1, 2020

In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer. For the Company, the amendment is effective January 1, 2020. Management does not expect that adoption of this guidance will have a significant impact on the Company’s financial statements.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement. ASU 2018-13 considers cost and benefits, and removes, modifies and adds disclosure requirements in Topic 820. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty is to be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments are to be applied retrospectively to all periods presented. ASU 2018-13 is effective for the Company for fiscal years beginning after December 15, 2019, including interim periods within that fiscal year and early adoption was permitted. Management does not expect that adoption of this guidance will have a significant impact on the Company’s financial statements.

New Accounting Pronouncements Not Yet Adopted

In December 2019, the FASB issued ASU 2019-12 Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which removes certain exceptions for intra period allocations, recognizing deferred taxes for investments and calculating income taxes in interim periods. This ASU also adds guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. The guidance is effective for the Company for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. Management is currently assessing the impact of this standard on the Company’s financial statements.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, an amendment which modifies the measurement and recognition of credit losses for most financial assets and certain other instruments. The amendment updates the guidance for measuring and recording credit losses on financial assets measured at amortized cost by replacing the “incurred loss” model with an “expected loss” model. Accordingly, these financial assets will be presented at the net amount expected to be collected. The amendment also requires that credit losses related to available-for-sale debt securities be recorded as an allowance through net income rather than reducing the carrying amount under the current, other-than-temporary-impairment model. For smaller reporting companies the guidance is effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. Early adoption is permitted. Management is currently assessing the impact of this standard on the Company’s financial statements.

Leases (Details)	12 Months Ended
Leases (Details)	Dec. 31, 2019 ft² lease	Oct. 31, 2018 ft²	Apr. 30, 2016 ft²
Lessee, Lease, Description [Line Items]
Number of operating lease arrangements \| lease	2
Area of office space \| ft²	10,716	3,520	72,500
Option to extend	true
Renewal term	5 years
Annual Escalation (as a percent)	3.00%
Weighted-average discount rate	12.99%
Weighted-average remaining life	1 year 9 months 18 days
Maximum [Member]
Lessee, Lease, Description [Line Items]
Threshold period for giving notice of lease extension	18 months
Minimum [Member]
Lessee, Lease, Description [Line Items]
Threshold period for giving notice of lease extension	12 months

Net Loss Per Share - Computation of Basic and Diluted Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss	$ (19,790)	$ (23,539)	$ (25,467)	$ (26,144)	$ (27,862)	$ (24,126)	$ (22,291)	$ (17,019)	$ (94,940)	$ (91,298)	$ (64,339)
Denominator:
Weighted average common shares outstanding - basic and diluted									64,478,066	56,219,919	47,435,331
Net loss per share - basic and diluted	$ (0.27)	$ (0.37)	$ (0.41)	$ (0.42)	$ (0.45)	$ (0.39)	$ (0.42)	$ (0.36)	$ (1.47)	$ (1.62)	$ (1.36)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets and Liabilities (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets:
Assets at fair value	$ 244,388	$ 164,356
Liabilities:
Derivative liability	969	585
Level 1 [Member]
Assets:
Assets at fair value	147,208	77,234
Level 2 [Member]
Assets:
Assets at fair value	97,180	87,122
Liabilities:
Derivative liability		52
Level 3 [Member]
Liabilities:
Derivative liability	969	533
Derivative Liability Exit Fee [Member]
Assets:
Assets at fair value		533
Liabilities:
Derivative liability	969
Derivative Liability Exit Fee [Member] \| Level 3 [Member]
Assets:
Assets at fair value		533
Liabilities:
Derivative liability	969
Foreign Currency Derivative Contracts [Member]
Assets:
Assets at fair value		52
Foreign Currency Derivative Contracts [Member] \| Level 2 [Member]
Assets:
Assets at fair value		52
Money Market Funds [Member]
Assets:
Assets at fair value	147,208	73,238
Money Market Funds [Member] \| Level 1 [Member]
Assets:
Assets at fair value	147,208	73,238
U.S. Treasury Securities [Member]
Assets:
Assets at fair value		3,996
U.S. Treasury Securities [Member] \| Level 1 [Member]
Assets:
Assets at fair value		3,996
Corporate Bonds [Member]
Assets:
Assets at fair value	33,134	34,590
Corporate Bonds [Member] \| Level 2 [Member]
Assets:
Assets at fair value	33,134	34,590
Commercial Paper [Member]
Assets:
Assets at fair value	56,041	43,154
Commercial Paper [Member] \| Level 2 [Member]
Assets:
Assets at fair value	56,041	43,154
Asset-Backed Securities [Member]
Assets:
Assets at fair value	8,005	9,378
Asset-Backed Securities [Member] \| Level 2 [Member]
Assets:
Assets at fair value	$ 8,005	$ 9,378

Warrants	12 Months Ended
Warrants	Dec. 31, 2019
Warrants
Warrants	9. WARRANTS Offering of Common Stock and Warrants In June 2015, the Company sold and issued an aggregate of 7,242,992 shares of its common stock and warrants to purchase 2,172,899 shares of common stock for aggregate gross proceeds of approximately $77.8 million or net proceeds, after deducting issuance costs, of approximately $74.3 million. The purchase price for the common stock was $10.70 per share and the purchase price for the warrants was $0.125 per warrant. The warrants are exercisable for an exercise price of $13.91 per share at any time prior to the earlier of (i) 5 years from the date of issuance or (ii) certain changes in control of the Company. The Company had determined that the warrants should be classified as equity. In July 2015, the Company filed a registration statement with the SEC with respect to the common stock and warrants. Other than with respect to warrants issued to holders affiliated with New Enterprise Associates, the warrants contain limitations that prevent each holder of warrants from acquiring shares upon exercise of the warrants that would cause the number of shares beneficially owned by it and its affiliates to exceed 9.99% of the total number of shares of the Company’s common stock then issued and outstanding. In addition, upon certain changes in control of the Company, each holder of a warrant can elect to receive, subject to certain limitations and assumptions, securities in a successor entity. None of the warrants issued in June 2015 have been exercised including during each of the years ended December 31, 2019, 2018 and 2017.

Property and Equipment - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and Equipment
Depreciation and amortization expense	$ 2.5	$ 2.7	$ 2.6

Commitments and Contingencies - Schedule of Future Minimum Payments Under Noncancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Property, Plant and Equipment [Line Items]
2020	$ 3,065
2021	2,183
Total undiscounted operating lease payments	5,248
Operating Equipment Leases
Property, Plant and Equipment [Line Items]
2020	3,121
2021	2,213
Total undiscounted operating lease payments	$ 5,334

Derivative Financial Instruments - Additional Information (Details) SFr in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2019 CHF (SFr)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Settlement of forward foreign currency exchange contract in the aggregate notional amount of Swiss francs		$ 436,000	$ 111,000
Gain (loss) on derivative instruments		$ 60,558	$ 124,194	$ 0
Foreign Currency Derivative Contracts [Member]
Derivative [Line Items]
Settlement of forward foreign currency exchange contract in the aggregate notional amount of Swiss francs \| SFr	SFr 3.3

Leases - Undiscounted Cash Payment Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Undiscounted cash payment obligations for its operating lease liabilities
2020	$ 3,065
2021	2,183
Total undiscounted operating lease payments	5,248
Imputed interest expenses	(564)
Total liabilities	4,684
Current portion of lease liabilities	2,608
Operating lease liability, net of current portion	2,076
Rent expense under operating leases	$ 2,592	$ 1,800	$ 1,700

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Selected Quarterly Financial Data (Unaudited)

Selected Quarterly Financial Data (Unaudited)

18. SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)

Selected quarterly financial results from operations for the years ended December 31, 2019 and 2018 are as follows (in thousands, except per share amounts):


	2019 Quarter Ended
	March 31		June 30		September 30		December 31
Total revenue	$	—	$	18	$	3,013	$	2,250
Gross profit	$	—	$	18	$	2,413	$	2,250
Operating expenses	$	25,498	$	24,846	$	24,502	$	21,098
Net loss	$	(26,144)	$	(25,467)	$	(23,539)	$	(19,790)
Net loss per share - basic and diluted	$	(0.42)	$	(0.41)	$	(0.37)	$	(0.27)


	2018 Quarter Ended
	March 31		June 30		September 30		December 31
Total revenue	$	2,320	$	30	$	172	$	85
Gross profit	$	1,856	$	30	$	170	$	85
Operating expenses	$	19,541	$	22,184	$	23,902	$	27,461
Net loss	$	(17,019)	$	(22,291)	$	(24,126)	$	(27,862)
Net loss per share - basic and diluted	$	(0.36)	$	(0.42)	$	(0.39)	$	(0.45)

Summary of Significant Accounting Policies - Impact of Adoption (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets	$ 3,970
Current portion of operating lease liability	2,608
Operating lease liability, net of current portion	2,076
Accrued expenses and other current liabilities	7,248		$ 12,857
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets		$ 5,810
Current portion of operating lease liability		1,892
Operating lease liability, net of current portion		4,684
Accrued expenses and other current liabilities		12,673	12,857
Other long-term liabilities			$ 582
Under Topic 840
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued expenses and other current liabilities	7,571
Other long-term liabilities	258
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets	3,970
Current portion of operating lease liability	2,608
Operating lease liability, net of current portion	2,076
Accrued expenses and other current liabilities	(323)
Other long-term liabilities	$ (258)
Effect of Change \| ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets		5,810
Current portion of operating lease liability		1,892
Operating lease liability, net of current portion		4,684
Accrued expenses and other current liabilities		(184)
Other long-term liabilities		$ (582)

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Liabilities and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Expenses and Other Current Liabilities
Accrued clinical and non-clinical expenses	$ 3,451	$ 9,790
Accrued contract manufacturing expenses	1,414	1,971
Derivative liability for exit fee	969	533
Accrued regulatory expenses	342	21
Accrued professional and consulting services	323	112
Foreign currency derivative contract		52
Other	749	378
Accrued liabilities and other liabilities	$ 7,248	$ 12,857

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments and Contingencies.

Commitments and Contingencies

17. COMMITMENTS AND CONTINGENCIES

Operating Leases

The Company has facility leases (see Note 12), as well as operating equipment leases. Future minimum payments on the Company’s noncancelable operating leases as of December 31, 2019 are as follows (in thousands):


Year Ended December 31,	Amounts
2020	$	3,121
2021		2,213
Total	$	5,334

Guarantees and Indemnifications

The Company indemnifies each of its officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at our request in such capacity, as permitted under Delaware law and in accordance with our certificate of incorporation and bylaws. The term of the indemnification period lasts as long as an officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity.

The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance, which allows the transfer of risk associated with our exposure and may enable the Company to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, the Company has not recognized any liabilities relating to these obligations for any period presented.

Legal Proceedings and Claims

From time to time the Company may be involved in claims arising in connection with its business. Based on information currently available, management believes that the amount, or range, of reasonably possible losses in connection with any pending actions against the Company will not be material to the Company’s financial condition or cash flows, and no contingent liabilities were accrued as of December 31, 2019 or 2018.

Fair Value Measurements - Additional Information (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Fair Value Measurements
Transfer of assets from Level 1 to Level 2	$ 0
Transfer of assets from Level 2 to Level 1	$ 0

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions					1 Months Ended
	Dec. 09, 2019	Nov. 22, 2019	Jun. 25, 2018	May 25, 2018	Dec. 31, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Common stock issued				14,375,000	88,817,741	62,516,627
Common stock, shares authorized					300,000,000	300,000,000
Common stock, par value					$ 0.0001	$ 0.0001
Public offering price	$ 6.25
Underwriting discounts and commissions					$ 8.9
Gross proceeds					143.8
Net proceeds					$ 134.9
Offering
Subsidiary, Sale of Stock [Line Items]
Common stock issued				12,500,000
Public offering price				$ 4.00
2019 offering
Subsidiary, Sale of Stock [Line Items]
Common stock issued	20,000,000
Underwriters' Option
Subsidiary, Sale of Stock [Line Items]
Common stock issued			1,875,000		3,000,000
Underwriting discounts and commissions			$ 3.7
Number of days to underwriters to sell additional common shares	30 days			30 days
Gross proceeds			57.5
Net proceeds			$ 53.8
Private Placement
Subsidiary, Sale of Stock [Line Items]
Common stock issued		2,873,563
Public offering price		$ 6.96
Net proceeds		$ 20.0
2019 Offering and Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Common stock issued					23,000,000

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended				12 Months Ended
	Jun. 18, 2014	Dec. 31, 2019	Nov. 30, 2018	Jul. 31, 2018	Jan. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period						4 years
Common stock reserved	1,454,549
Maximum shares to be issued up on exercise of incentive stock options	1,153,279
Number of options granted during the period						2,362,685
Weighted-average grant-date estimated fair value of options granted						$ 1.79	$ 4.29	$ 8.19
Fair Value of exercise price		7.51				7.51
Estimated fair value of options exercised during period						$ 400	$ 0	$ 300
Estimated fair value of restricted stock vested during period						200	600	400
Stock based compensation expenses						$ 9,936	$ 9,226	$ 9,590
Shares available for future grant		1,196,746				1,196,746	608,528
Proceeds from issuance of common stock, net of issuance costs		$ 134,900
Purchase price of common shares										$ 10.70
Warrants issued to purchase common stock										2,172,899
Exercise price for warrants		$ 13.91				$ 13.91				$ 13.91
Issuance of common stock for services, shares						113,136	75,183	46,858
Issuance of common stock for services, amount						$ 312	$ 303
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Expense		$ 53				$ 53
Average Vesting Period						2 months 12 days
2014 Equity Incentive Award Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved	1,419,328
Maximum shares to be issued up on exercise of incentive stock options						10,683,053
Possible increase in shares reserved for issuance as percentage of outstanding stock						4.00%
2008 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares reserved for issuance	35,221
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved	202,762
Maximum shares to be issued up on exercise of incentive stock options						2,230,374
Possible increase in shares reserved for issuance as percentage of outstanding stock						1.00%
Shares available for future grant		519,578				519,578	680,322
2016 Employment Commencement Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options granted during the period						0
2016 Employment Commencement Incentive Plan [Member] \| Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved									1,000,000
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Expense		$ 8,277				$ 8,277
Average Vesting Period						2 years 6 months
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expenses						$ 300	$ 900	$ 900
Service Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding							85,609
Number of vested shares						85,609
Performance-Based Restricted Stock Units (PRSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expenses						$ 2,400	$ 0
Unrecognized Compensation Expense		$ 965				$ 965
Average Vesting Period						8 months 12 days
Number of Shares, Granted				903,374	161,865
Number of Shares, Outstanding		849,757				849,757	894,764
Number of vested shares			125,895			0
Recognized stock-based compensation related expense in connection with vesting of award granted						$ 0	$ 600	$ 1,000

Cash, Cash Equivalents and Short-Term Investments - Schedule of Securities Classified as Cash, Cash Equivalents and Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	$ 181,133	$ 78,768	$ 75,383	$ 74,598
Cash and cash equivalents, Amortized Cost	181,130
Cash and cash equivalents, Gross Unrealized Gains	3
Cash and cash equivalents, Fair Value	181,133	78,768
Short-term investments, Amortized Cost	66,362	89,359
Short-term investments, Gross Unrealized Gains	20
Short-term investments, Gross Unrealized Losses	(3)	(38)
Short-term investments, Fair Value	66,379	89,321
Cash equivalents and short-term investments, Amortized Cost	247,492	168,127
Cash equivalents and short-term investments, Gross Unrealized Gains	23
Cash equivalents and short-term investments, Gross Unrealized Losses	(3)	(38)
Cash equivalents and short-term investments, Fair Value	247,512	168,089
Cash [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	3,124	3,733
Cash and cash equivalents, Fair Value	3,124	3,733
Money Market Funds [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	147,208	73,238
Cash and cash equivalents, Fair Value	147,208	73,238
Corporate Bonds (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	11,441
Cash and cash equivalents, Fair Value	11,441
Commercial Paper (Cash Equivalents) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	19,357	1,797
Cash and cash equivalents, Gross Unrealized Gains	3
Cash and cash equivalents, Fair Value	19,360	1,797
U.S. Treasury Securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost		3,996
Cash and cash equivalents, Fair Value		3,996
Corporate Bonds (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	21,690	34,611
Short-term investments, Gross Unrealized Gains	6
Short-term investments, Gross Unrealized Losses	(3)	(21)
Short-term investments, Fair Value	21,693	34,590
Commercial Paper (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	36,667	41,371
Short-term investments, Gross Unrealized Gains	14
Short-term investments, Gross Unrealized Losses		(14)
Short-term investments, Fair Value	36,681	41,357
Asset-Backed Securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	8,005	9,381
Short-term investments, Gross Unrealized Losses		(3)
Short-term investments, Fair Value	$ 8,005	$ 9,378

Equity Incentive Plans - Unrecognized Stock-Based Compensation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Expense	$ 8,277
Average Vesting Period	2 years 6 months
Performance-Based Restricted Stock Units (PRSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Expense	$ 965
Average Vesting Period	8 months 12 days
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation Expense	$ 53
Average Vesting Period	2 months 12 days

Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Change in valuation allowance	(21.90%)	(22.50%)	19.90%
Income tax at the federal statutory rate	21.00%	21.00%	35.00%
State taxes, net of federal benefit	0.30%	0.60%	0.50%
Net impact related to foreign subsidiary			(0.012)
Impact of tax reform rate change			(56.40%)
Tax credits	1.60%	1.40%	1.00%
Stock based compensation	(0.90%)	(1.20%)	(0.80%)
Other	(0.40%)	0.70%	0.10%
Income tax provision	(0.30%)	0.00%	(1.90%)

Leases

12 Months Ended

Dec. 31, 2019

Leases

Leases

12. LEASES

The Company has obtained the right of use for office space assets under two operating lease agreements. The Company has evaluated its facility leases and determined that, effective upon the adoption of Topic 842, the leases evaluated are all operating leases. The Company has performed an evaluation of its other contracts with suppliers and collaborators in accordance with Topic 842 and has determined that, except for the facility leases described below, none of the Company’s contracts contain a lease.

The Company obtained the right of use of office space located in Fremont, California, under a lease agreement entered into in September 2008 that was amended in December 2012 to extend the lease agreement to September 2016. In September 2014, the Company signed the second amendment to its facility lease agreement to add space and to extend the lease term through September 2019. In May 2016, the Company signed a third amendment to its facility lease agreement in Fremont, California to add space and to extend the lease term through September 2021 (the “Third Amendment”). The office space consists of 72,500 square feet, that includes an additional 10,716 square feet added in September 2019, with the entire lease terminating on September 10, 2021. The Company has an option to extend the term by five years as to the entire premises at the higher of (i) a 3% annual escalation of the then-current base rent and (ii) the then-current fair market value for comparable premises, by giving written notice of its election to exercise such option at least 12 months but not more than 18 months prior to the end of the expiration of the lease term. This option to extend the lease term by five years has not been included in the calculation since currently the exercise of the option is uncertain and therefore deemed not probable. The Company also obtained the right of use of 3,520 square feet of office space located in Waltham, Massachusetts, in October 2018 that terminates on September 30, 2021.

All of the Company’s leases are operating leases. Certain of the leases have both lease and non-lease components. The Company has elected to account for each separate lease component and the non-lease components associated with that lease component as a single lease component for all classes of underlying assets. As of December 31, 2019, the weighted average discount rate used for the calculations was 12.99% and the weighted average remaining lease term was 1.8 years.

The following table provides additional details of the leases presented in the balance sheets (in thousands except remaining life and discount rate):


	December 31, 2019
Facilities
Right of use assets	$	3,970

Current portion of lease liabilities		2,608
Operating lease liability, net of current portion		2,076
Total liabilities	$	4,684

Weighted-average remaining life		1.8	years
Weighted-average discount rate		12.99	%

The lease costs, which are included in operating expenses in our statements of operations, were as follows (in thousands):


	Year Ended
	December 31, 2019
Facilities
Operating lease cost	$	2,592
Cash paid for operating lease	$	2,645

The following table summarizes the Company’s undiscounted cash payment obligations for its operating lease liabilities as of December 30, 2019 (in thousands):


Years Ending December 31,
2020	$	3,065
2021		2,183
Total undiscounted operating lease payments		5,248
Imputed interest expenses		(564)
Total operating lease liabilities		4,684
Less: Current portion of operating lease liability		2,608
Operating lease liability, net of current portion	$	2,076

Rent expense under operating leases was $2.6 million, $1.8 million and $1.7 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Results from Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Data (Unaudited)
Total revenue	$ 2,250	$ 3,013	$ 18		$ 85	$ 172	$ 30	$ 2,320	$ 5,281	$ 2,607	$ 42,000
Gross profit	2,250	2,413	18		85	170	30	1,856	4,681	2,141	33,600
Operating expenses	21,098	24,502	24,846	$ 25,498	27,461	23,902	22,184	19,541	95,944	93,088	98,715
Net loss	$ (19,790)	$ (23,539)	$ (25,467)	$ (26,144)	$ (27,862)	$ (24,126)	$ (22,291)	$ (17,019)	$ (94,940)	$ (91,298)	$ (64,339)
Net (loss) income per share:
Net loss per share - basic and diluted	$ (0.27)	$ (0.37)	$ (0.41)	$ (0.42)	$ (0.45)	$ (0.39)	$ (0.42)	$ (0.36)	$ (1.47)	$ (1.62)	$ (1.36)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Cash, Cash Equivalents and Short-Term Investments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash Cash Equivalents And Short Term Investments [Line Items]
Investment in continuous unrealized loss position for more than one year	$ 0	$ 0
Maximum [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available for sale securities contractual maturity period	1 year

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2019
Stockholders' Equity
Stockholders' Equity	7. STOCKHOLDERS’ EQUITY On December 9, 2019, the Company completed an underwritten public offering of 20,000,000 shares of common stock at a price of $6.25 per share before underwriting discounts and commissions, or the 2019 Offering. In connection with the 2019 Offering, the Company entered into an underwriting agreement, or the 2019 Underwriting Agreement, with Citigroup Global Markets Inc., Cowen and Company LLC, SVB Leerink LLC and Piper Jaffray & Co., or collectively the 2019 Underwriters, pursuant to which the Company granted to the 2019 Underwriters a 30-day option to purchase up to an additional 3,000,000 shares of the Company’s common stock, or the 2019 Overallotment. The Company completed the sale of 23,000,000 shares, inclusive of the 2019 Overallotment, to the 2019 Underwriters and that sale resulted in the receipt by the Company of aggregate gross proceeds of approximately $143.8 million, less underwriting discounts, commissions and offering expenses totaling approximately $8.9 million, which resulted in net proceeds of approximately $134.9 million. On November 22, 2019, the Company and KKC entered into a stock purchase agreement, pursuant to which the Company sold an aggregate of 2,873,563 shares of its common stock at $6.96 per share for net proceeds of approximately $20.0 million, or the Private Placement. The Private Placement closed on November 25, 2019. On May 25, 2018, the Company completed an underwritten public offering of 12,500,000 shares of common stock at a price of $4.00 per share before underwriting discounts and commissions, or the 2018 Offering. In connection with the 2018 Offering, the Company entered into an underwriting agreement, or the 2018 Underwriting Agreement, with Jefferies LLC and SVB Leerink (formerly known as Leerink Partners LLC), or together the 2018 Underwriters, pursuant to which the Company granted to the 2018 Underwriters a 30-day option to purchase up to an additional 1,875,000 shares of the Company’s common stock, or the 2018 Overallotment. The Company completed the sale of 14,375,000 shares, inclusive of the 2018 Overallotment, to the 2018 Underwriters, and that sale resulted in the receipt by the Company of aggregate gross proceeds of approximately $57.5 million, less underwriting discounts, commissions and offering expenses totaling approximately $3.7 million, which resulted in net proceeds of approximately $53.8 million.

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Commitments and Contingencies.
Contingent liabilities	$ 0	$ 0

Geographic Information and Concentrations

12 Months Ended

Dec. 31, 2019

Geographic Information and Concentrations

Geographic Information and Concentrations

15. GEOGRAPHIC INFORMATION AND CONCENTRATIONS

Revenue by geographic areas for the years ended December 31, 2019, 2018 and 2017, are as follows (in thousands):


	Year Ended December 31,
	2019		2018		2017
United States	$	—	$	—	$	—
International:
North America (1)		—		2,320		—
Asia Pacific (2) (3) (4)		5,281		287		42,000
Total revenue	$	5,281	$	2,607	$	42,000

(1)Revenues from North America in 2018 comprised of $2.3 million from Canada in accordance with the Knight Agreement.

(3) Revenues from Asia Pacific in 2018 comprised $0.3 million from Japan in accordance with the 2017 KKC Agreement.

(4) Revenues from Asia Pacific in 2017 included $30.0 million from Japan in accordance with the 2017 KKC Agreement and $12.0 million from China in accordance with the Fosun Agreement.

Revenues are attributed to geographical areas based on the domicile of the Company’s collaboration partners.

Revenues recorded in the years ended December 31, 2019, 2018 and 2017, were wholly from collaboration partnerships. Collaboration partnerships accounting for more than 10% of total revenues during the years ended December 31, 2019, 2018 and 2017, are as follows:


	Year Ended December 31,
	2019		2018		2017
Fosun Pharma	57	%	—		29	%
XuanZhu	28	%	—		—
KKC	15	%	11	%	71	%
Knight	—		89	%	—

Equity Incentive Plans

12 Months Ended

Dec. 31, 2019

Equity Incentive Plans

Equity Incentive Plans

8. EQUITY INCENTIVE PLANS

2008 Plan

The Company granted options under its 2008 Stock Incentive Plan (the “2008 Plan”) until June 2014 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2008 Plan. The 2008 Plan provided for the granting of incentive and non-qualified stock options, and stock purchase rights to employees, directors and consultants at the discretion of the Board of Directors. Stock options granted generally vest over a period of four years from the date of grant. In connection with the Board of Directors and stockholders’ approval of the 2014 Plan, all remaining shares available for future award under the 2008 Plan were transferred to 2014 Plan, and the 2008 Plan was terminated.

2014 Plan

The 2014 Equity Incentive Award Plan (the “2014 Plan”) became effective on June 18, 2014. Under the 2014 Plan, 1,419,328 shares of common stock were initially reserved for issuance pursuant to a variety of stock-based compensation awards, including stock options, stock appreciation rights, or SARs, restricted stock awards, service-based restricted stock unit (“RSU”) awards, performance-based restricted stock unit (“PRSU”) awards, deferred stock awards, deferred stock unit awards, dividend equivalent awards, stock payment awards and performance awards. In addition, 35,221 shares that had been available for future awards under the 2008 Plan as of June 18, 2014, were added to the initial reserve available under the 2014 Plan, bringing the total reserve upon the effective date of the 2014 Plan to 1,454,549. The number of shares initially reserved for issuance or transfer pursuant to awards under the 2014 Plan will be increased by (i) the number of shares represented by awards outstanding under 2008 Plan on June 18, 2014, that are either forfeited or lapse unexercised or that are repurchased for the original purchase price thereof, up to a maximum of 1,153,279 shares, and (ii) if approved by the Administrator of the 2014 Plan, an annual increase on the first day of each fiscal year ending in 2024 equal to the lesser of (A) four percent (4.0%) of the shares of stock outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (B) such smaller number of shares of stock as determined by our board of directors; provided, however, that no more than 10,683,053 shares of stock may be issued upon the exercise of incentive stock options.

2016 Plan

In November 2016, the Company’s board of directors approved the 2016 Employment Commencement Incentive Plan (the “Inducement Plan”) under which 1,000,000 shares were reserved. As of December 31, 2019, no shares of the Company’s common stock were subject to inducement grants that were issued pursuant to the Inducement Plan.

Stock Plan Activity

The following table summarizes activity under the 2008 Plan and the 2014 Plan, including grants issued to nonemployees, in the year ended December 31, 2019:


		Options Issued and Outstanding			Weighted
			Weighted-Average		Average
	Shares Available		Exercise Price per		Remaining	Aggregate
	for Grant	Number of Shares	Share		Contractual Term	Intrinsic Value
					(in Years)	(in thousands)
Balance at December 31, 2018	608,528	5,506,760	$	8.32
Options authorized	2,490,417	—	$	—
Options granted	(2,362,685)	2,362,685	$	2.56
Options exercised	—	(68,062)	$	2.59
Options canceled	528,615	(528,615)	$	7.69
Issuance of common stock for services	(113,136)	—		—
Forfeitures of PRSUs granted in prior years	45,007	—		—
Balance at December 31, 2019	1,196,746	7,272,768	$	6.55	7.40	$	19,128
Vested and expected to vest at December 31, 2019		6,754,711	$	6.74	7.30	$	17,217
Exercisable at December 31, 2019		4,183,281	$	7.95	6.46	$	8,753

The aggregate intrinsic value represents the difference between the total pre-tax value (i.e., the difference between the Company’s stock price and the exercise price) of stock options outstanding as of December 31, 2019, based on the Company’s common stock closing price of $7.51 per share, which would have been received by the option holders had all their in-the-money options been exercised as of that date.

The intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017, was $0.4 million, zero, and $0.3 million, respectively.

The weighted-average grant-date estimated fair value of options granted during the years ended December 31, 2019, 2018 and 2017 was $1.79, $4.29 and $8.19 per share, respectively. The estimated grant date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following weighted-average assumptions:


	Year Ended December 31,
	2019
Expected term (years)	6.00
Expected volatility	81	%
Risk-free interest rate	2.42	%
Dividend yield	—	%

Expected Term—The Company has limited historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock-option grants. As such, the expected term was estimated using the simplified method whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option.

Expected Volatility—Since January 1, 2017, the Company has used the historic volatility of its own stock over the retrospective period corresponding to the expected remaining term of the options, or the period since its shares were first quoted on The Nasdaq Global Market, if that is shorter, to compute its expected stock price volatility.

Risk-Free Interest Rate—The risk-free interest rate assumption is based on the zero-coupon U.S. treasury instruments on the date of grant with a maturity date consistent with the expected term of the Company’s stock option grants.

Dividend Yield—To date, the Company has not declared or paid any cash dividends and does not have any plans to do so in the future. Therefore, the Company used an expected dividend yield of zero.

Restricted Stock Units

The following table summarizes restricted stock unit activity under the 2014 Plan in the year ended December 31, 2019, and includes restricted stock units with time or service-based vesting and those restricted stock units with performance-based vesting:


					Weighted-
		Weighted-Average			Average Grant
	Number of	Grant Date Fair		Number of	Date Fair Value
	RSUs	Value Per Share		PRSUs	Per Share
Non-vested restricted stock units at December 31, 2018	85,609	$	4.70	894,764	$	4.30
Granted	—	$	—	—	$	—
Vested	(85,609)	$	4.70	—	$	—
Forfeited	—	$	—	(45,007)	$	4.30
Non-vested restricted stock units at December 31, 2019	—	$	—	849,757	$	4.30

RSUs and PRSUs are generally subject to forfeiture if employment terminates prior to the release of vesting restrictions. The related compensation expense, which is based on the grant date fair value of the Company’s common stock multiplied by the number of units granted, is recognized ratably over the period during which the vesting restrictions lapse.

In January 2017, the Company granted 161,865 PRSUs to certain employees that vested upon the achievement of specified performance conditions, subject to the employees’ continued service relationship with the Company through the date of achievement, of which 125,895 PRSUs vested in November 2018. None of these PRSUs vested during the year ended December 31, 2017. The related compensation cost was recognized as an expense over the estimated vesting period ratably after achievement of the milestone was deemed probable. The expense recognized for these awards was based on the grant date fair value of the Company’s common stock multiplied by the number of units granted. The Company recognized zero, $0.6 million and $1.0 million of related expense during the year ended December 31, 2019, 2018 and 2017, respectively.

In July 2018, the Company granted 903,374 PRSUs to its employees that vest upon the achievement of certain performance conditions, subject to the employees’ continued service relationship with the Company through the achievement date. At December 31, 2019, 849,757 of these PRSUs were outstanding and none vested. Based on the evaluation of the performance conditions at December 31, 2019, the Company recorded stock-based compensation expense of $2.4 million for the year ended December 31, 2019. Stock-based compensation expense recorded related to these PRSUs were zero for the year ended December 31, 2018. The related compensation cost was recognized as an expense over the estimated vesting period ratably when achievement of the milestone was considered probable. The expense recognized for these awards is based on the grant date fair value of the Company’s common stock multiplied by the number of units granted.

With respect to RSUs, we recognize expense over the estimated vesting period ratably, contingent on continued service. The Company recognized $0.3 million, $0.9 million and $0.9 million of related expense during the year ended December 31, 2019, 2018 and 2017, respectively. The total estimated fair value of RSUs vested during the years ended December 31, 2019, 2018 and 2017 was $0.2 million, $0.6 million and $0.4 million, respectively.

Issuance of Common Stock for Services

During the years ended December 31, 2019, 2018 and 2017, the Company issued 113,136, 75,183 and 46,858 shares, respectively, of common stock to members of the board of directors who elected to receive stock in lieu of their cash fees under the Company’s Non-Employee Director Compensation Program. The shares issued during the years ended December 31, 2019, 2018 and 2017 were valued at $0.3 million, $0.3 million and $0.2 million, respectively, based on the fair value of the common stock on the date of grant.

Employee Stock Purchase Plan

The Company adopted the 2014 Employee Stock Purchase Plan (“ESPP”) and initially reserved 202,762 shares of common stock as of its effective date of June 18, 2014. If approved by the Administrator of the ESPP, on the first day of each calendar year, ending in 2024, the number of shares in the reserve will increase by an amount equal to the lesser of (i) one percent (1.0%) of the shares of common stock outstanding on the last day of the immediately preceding fiscal year and (ii) such number of shares of common stock as determined by the board of directors; provided, however, no more than 2,230,374 shares of our common stock may be issued under the ESPP.

The following table summarizes ESPP activity in the year ended December 31, 2019:


	Shares Available	Number of Shares	Purchase Price
	for Grant	Purchased	per Share		Gross Proceeds
					(in thousands)
Balance at December 31, 2018	680,322	330,936
Shares purchased	(160,744)	160,744	$	2.48	$	396
Balance at December 31, 2019	519,578	491,680

The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of ESPP purchase rights granted to employees:


	Year Ended December 31,
	2019
Expected term (years)	0.5
Expected volatility	69	%
Risk-free interest rate	2.20	%
Dividend yield	—	%

Stock-based Compensation

Total stock-based compensation recognized was as follows:


	Year Ended December 31,
	2019		2018			2017
	(in thousands)
Research and development	$	4,104	$	3,666	$	4,585
General and administrative		5,832		5,560		5,005
Total	$	9,936	$	9,226	$	9,590

At December 31, 2019, the Company had total unrecognized stock-based compensation expense, net of estimated forfeitures, of the following:



	At December 31, 2019
	Unrecognized Compensation Expense		Average Vesting Period
	(in thousands)		(Years)
Stock options grants	$	8,277	2.5
PRSU grants	$	965	0.7
ESPP	$	53	0.2

Geographic Information and Concentrations (Details) - USD ($) $ in Thousands	3 Months Ended							12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 2,250	$ 3,013	$ 18	$ 85	$ 172	$ 30	$ 2,320	$ 5,281	$ 2,607	$ 42,000
North America
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									2,320
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue								5,281	287	42,000
HONG KONG
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue								1,500
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue								3,000		12,000
KKC \| Japan \| 2019 KKC Agreement
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue								300
KKC \| Japan \| 2017 KKC Agreement
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue								$ 500	$ 300	$ 30,000

Borrowings (Details) - USD ($) $ in Thousands		12 Months Ended
Borrowings (Details) - USD ($) $ in Thousands	May 16, 2018	Dec. 31, 2018	Dec. 31, 2019
Term Loans
Amount of term loan facility	$ 50,000		$ 51,975
Net proceeds from the loan	$ 49,300	$ 49,292
Percentage of premium payable on redemption of the term loan	1.00%
Amount of fee payable upon closing of the term loan	$ 500
Additional default interest rate	4.00%
Future debt payment obligations
2020			2,083
2021			25,000
2022			24,892
Total principal and final fee payments	$ 50,000		51,975
Less: Unamortized discount and debt issuance costs			(741)
Less: Unaccreted value of final fee			(1,220)
Loan payable			50,014
Loan payable, current portion			1,183
Loan payable, net of current portion		$ 49,209	$ 48,831
At Maturity
Term Loans
Final payment fee (as a percent)	3.95%
Prior to first anniversary of closing date
Term Loans
Prepayment fee (as a percent)	3.00%
After first anniversary of closing date
Term Loans
Prepayment fee (as a percent)	2.00%
After second anniversary to maturity date
Term Loans
Prepayment fee (as a percent)	1.00%
LIBOR
Term Loans
Floating interest rate	7.45%

Organization and Basis of Presentation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 segment
Organization and Basis of Presentation
Number of operating segments	1

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Taxes

Summary of Components of the Provision for Income Taxes

The components of the provision for income taxes for the year ended December 31, 2019, 2018 and 2017, are as follows (in thousands):


	Year Ended December 31,
	2019		2018		2017
Current:
State	$	2	$	4	$	5
Foreign		301		—		1,204
Total current		303		4		1,209
Deferred:
Federal		—		—		(30)
Total deferred		—		—		(30)
Provision for income taxes	$	303	$	4	$	1,179

Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate


	Year Ended December 31,
	2019		2018		2017
Change in valuation allowance	(21.9)	%	(22.5)	%	19.9	%
Income tax at the federal statutory rate	21.0		21.0		35.0
State taxes, net of federal benefit	0.3		0.6		0.5
Net impact related to foreign subsidiary	—		—		(1.2)
Impact of tax reform rate change	—		—		(56.4)
Tax credits	1.6		1.4		1.0
Stock based compensation	(0.9)		(1.2)		(0.8)
Other	(0.4)		0.7		0.1
Income tax provision	(0.3)	%	—	%	(1.9)	%

Significant Components of the Company's Deferred Tax Assets


	December 31,
	2019		2018
	(in thousands)
Deferred tax assets:
Amortization and depreciation	$	45,555	$	38,376
Net operating loss carryforwards		40,896		31,621
Tax credits		10,136		8,200
Stock-based compensation		4,853		3,763
Lease obligation		984		—
Other		940		888
Gross deferred tax assets		103,364		82,848
Valuation allowance		(102,344)		(81,645)
Deferred tax assets net of valuation allowance		1,020		1,203
Deferred tax liabilities
Right of use asset		(834)		—
Revenue recognition		(158)		(1,054)
Other		(28)		(149)
Net deferred tax assets	$	—	$	—

Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits


	December 31,
	2019		2018		2017
	(in thousands)
Balance at beginning of year	$	23,052	$	20,734	$	3,892
Additions based on tax positions related to prior year		755		1,634		16,103
Additions based on tax positions related to current year		731		684		739
Balance at end of year	$	24,538	$	23,052	$	20,734

Summary of Significant Accounting Policies - Cumulative adjustments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Reduction in accrued and other liabilities
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Correction of cumulative errors	$ 3.6
Reduction in research and development expenses
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Correction of cumulative errors	$ 3.6

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2019	Mar. 03, 2020	Jun. 30, 2019
Document And Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity Registrant Name	ARDELYX, INC.
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 125,911,696
Entity Common Stock, Shares Outstanding		88,929,668
Entity Central Index Key	0001437402
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Trading Symbol	ARDX

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2019

Property and Equipment

Summary of Property and Equipment


	December 31,
	2019		2018
	(in thousands)
Laboratory equipment	$	7,243	$	6,965
Office equipment and furniture		870		889
Leasehold improvements		7,949		7,949
Property and equipment, gross		16,062		15,803
Less: accumulated depreciation		(12,626)		(10,192)
Total property and equipment, net	$	3,436	$	5,611

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Taxes

Income Taxes

14. INCOME TAXES

The components of the provision for income taxes for the year ended December 31, 2019, 2018 and 2017, are as follows (in thousands):


	Year Ended December 31,
	2019		2018		2017
Current:
State	$	2	$	4	$	5
Foreign		301		—		1,204
Total current		303		4		1,209
Deferred:
Federal		—		—		(30)
Total deferred		—		—		(30)
Provision for income taxes	$	303	$	4	$	1,179

The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate:


	Year Ended December 31,
	2019		2018		2017
Change in valuation allowance	(21.9)	%	(22.5)	%	19.9	%
Income tax at the federal statutory rate	21.0		21.0		35.0
State taxes, net of federal benefit	0.3		0.6		0.5
Net impact related to foreign subsidiary	—		—		(1.2)
Impact of tax reform rate change	—		—		(56.4)
Tax credits	1.6		1.4		1.0
Stock based compensation	(0.9)		(1.2)		(0.8)
Other	(0.4)		0.7		0.1
Income tax provision	(0.3)	%	—	%	(1.9)	%

Deferred income taxes reflect the tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets are as follows as of December 31, 2019 and 2018:


	December 31,
	2019		2018
	(in thousands)
Deferred tax assets:
Amortization and depreciation	$	45,555	$	38,376
Net operating loss carryforwards		40,896		31,621
Tax credits		10,136		8,200
Stock-based compensation		4,853		3,763
Lease obligation		984		—
Other		940		888
Gross deferred tax assets		103,364		82,848
Valuation allowance		(102,344)		(81,645)
Deferred tax assets net of valuation allowance		1,020		1,203
Deferred tax liabilities
Right of use asset		(834)		—
Revenue recognition		(158)		(1,054)
Other		(28)		(149)
Net deferred tax assets	$	—	$	—

Realization of deferred tax assets is dependent on future taxable income, if any, the timing and the amount of which are uncertain. The Company assesses the available positive and negative evidence to estimate whether sufficient future taxable income will be generated to permit use of the existing deferred tax assets. A significant component of objective negative evidence evaluated was the Company’s cumulative loss incurred over the three-year period ended December 31, 2019. Such objective evidence limits the ability to consider other subjective evidence, such as our projections for future growth. On the basis of this evaluation, as of December 31, 2019, December 31, 2018 and December 31, 2017, a full valuation allowance has been recorded against Company’s net deferred tax asset. The amount of the deferred tax asset considered realizable, however, could be adjusted if estimates of future taxable income during the carryforward period are reduced or increased or if objective negative evidence in the form of cumulative losses is no longer present and additional weight is given to subjective evidence such as our projections for growth.

As of December 31, 2019, the Company had net operating loss carryforwards for federal income tax purposes of approximately $232.1 million, of which approximately $91.4 million can be carried forward indefinitely and the remaining net operating losses expire beginning in 2030, if not utilized. Federal research and development tax credit carryforwards of approximately $11.4 million that expire beginning in 2027, if not utilized, and foreign tax credit carryforwards of approximately $1.2 million that expire in 2027, if not utilized.

In addition, the Company had net operating loss carryforwards for California income tax purposes of approximately $88.3 million that expire beginning of 2030, if not utilized, and state research and development tax credit carryforwards of approximately $7.8 million which can be carried forward indefinitely. The Company had approximately $0.1 million of minimum tax credit carryovers for California income tax purposes. The minimum tax credits have no expiration date. The Company had other state net operating losses of approximately $1.8 million that begin to expire in 2025.

The future utilization of net operating loss and tax credit carryforwards and credits may be subject to an annual limitation, pursuant to Internal Revenue Code Sections 382 and 383, as a result of ownership changes that may have occurred previously or that could occur in the future. Due to the existence of the valuation allowance, limitations under Section 382 and 383 will not impact the Company’s effective tax rate.

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:


	December 31,
	2019		2018		2017
	(in thousands)
Balance at beginning of year	$	23,052	$	20,734	$	3,892
Additions based on tax positions related to prior year		755		1,634		16,103
Additions based on tax positions related to current year		731		684		739
Balance at end of year	$	24,538	$	23,052	$	20,734

The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $13.2 million, $9.8 million, and $8.6 million as of December 31, 2019, 2018, and 2017, respectively.

The Company has elected to include interest and penalties as a component of tax expense. During the years ended December 31, 2019, 2018 and 2017, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. Although the timing and outcome of an income tax audit is highly uncertain, the Company does not anticipate that the amount of existing unrecognized tax benefits will significantly change during the next 12 months.

The Company files a federal income tax return in the U.S. and state income tax returns in California, Georgia, Maryland, Massachusetts, Michigan, New Hampshire, Oregon and Wisconsin. Because carryforward attributes generated in past years may be adjusted in a future period, the income tax returns remain open to U.S. federal and California state tax examinations. The Company is not currently under examination in any tax jurisdiction.

Geographic Information and Concentrations - Concentration Risk (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fosun Pharma
Concentration Risk [Line Items]
Percentage of revenue	57.00%		29.00%
XuanZhu
Concentration Risk [Line Items]
Percentage of revenue	28.00%
KKC
Concentration Risk [Line Items]
Percentage of revenue	15.00%	11.00%	71.00%
Knight
Concentration Risk [Line Items]
Percentage of revenue		89.00%

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Balance Sheets
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	88,817,741	62,516,627
Common stock, shares outstanding	88,817,741	62,516,627

Organization and Basis of Presentation	12 Months Ended
Organization and Basis of Presentation	Dec. 31, 2019
Organization and Basis of Presentation
Organization and Basis of Presentation	1. ORGANIZATION AND BASIS OF PRESENTATION Ardelyx, Inc. (the “Company,” “we,” “us” or “our”) is a specialized biopharmaceutical company focused on developing first-in-class medicines to improve treatment choices for people with cardiorenal diseases. The Company operates in only one business segment, which is the research and development of biopharmaceutical products.

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Selected Quarterly Financial Data (Unaudited)

Schedule of Selected Quarterly Financial Results from Operations

Selected quarterly financial results from operations for the years ended December 31, 2019 and 2018 are as follows (in thousands, except per share amounts):


	2019 Quarter Ended
	March 31		June 30		September 30		December 31
Total revenue	$	—	$	18	$	3,013	$	2,250
Gross profit	$	—	$	18	$	2,413	$	2,250
Operating expenses	$	25,498	$	24,846	$	24,502	$	21,098
Net loss	$	(26,144)	$	(25,467)	$	(23,539)	$	(19,790)
Net loss per share - basic and diluted	$	(0.42)	$	(0.41)	$	(0.37)	$	(0.27)


	2018 Quarter Ended
	March 31		June 30		September 30		December 31
Total revenue	$	2,320	$	30	$	172	$	85
Gross profit	$	1,856	$	30	$	170	$	85
Operating expenses	$	19,541	$	22,184	$	23,902	$	27,461
Net loss	$	(17,019)	$	(22,291)	$	(24,126)	$	(27,862)
Net loss per share - basic and diluted	$	(0.36)	$	(0.42)	$	(0.39)	$	(0.45)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Summary of Significant Accounting Policies

Basis of Presentation

The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

Prior Period Errors

Use of Estimates

Liquidity

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with an original maturity date of 90 days or less on the date of purchase to be cash equivalents.

Short-Term Investments

Concentration of Credit Risk

Accounts Receivable

Foreign Currency and Forward Contracts

Property and Equipment

Impairment of Long-Lived Assets

Income Taxes

Revenue Recognition

Research and Development Costs

Accrued Research and Development Expenses

contract research organizations, or CROs, in connection with clinical studies;

investigative sites in connection with clinical studies;

vendors related to product manufacturing, development and distribution of clinical supplies; and

vendors in connection with preclinical development activities.

Stock-Based Compensation

Derivatives and Hedging Activities

Leases

Comprehensive Loss

Net Loss per Share

Leases (Tables)

12 Months Ended

Dec. 31, 2019

Leases

Summary of Additional Details of the Leases

The following table provides additional details of the leases presented in the balance sheets (in thousands except remaining life and discount rate):


	December 31, 2019
Facilities
Right of use assets	$	3,970

Current portion of lease liabilities		2,608
Operating lease liability, net of current portion		2,076
Total liabilities	$	4,684

Weighted-average remaining life		1.8	years
Weighted-average discount rate		12.99	%

Summary of Lease Costs

The lease costs, which are included in operating expenses in our statements of operations, were as follows (in thousands):


	Year Ended
	December 31, 2019
Facilities
Operating lease cost	$	2,592
Cash paid for operating lease	$	2,645

Summary of Undiscounted Cash Payment Obligations for Operating Lease Liabilities

The following table summarizes the Company’s undiscounted cash payment obligations for its operating lease liabilities as of December 30, 2019 (in thousands):


Years Ending December 31,
2020	$	3,065
2021		2,183
Total undiscounted operating lease payments		5,248
Imputed interest expenses		(564)
Total operating lease liabilities		4,684
Less: Current portion of operating lease liability		2,608
Operating lease liability, net of current portion	$	2,076

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2019

Accrued Expenses and Other Current Liabilities

Accrued Expenses and Other Current Liabilities

11. ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES

Accrued expenses and other current liabilities consist of the following (in thousands):


	December 31,		December 31,
	2019		2018
Accrued clinical and non-clinical expenses	$	3,451	$	9,790
Accrued contract manufacturing expenses		1,414		1,971
Derivative liability for exit fee		969		533
Accrued regulatory expenses		342		21
Accrued professional and consulting services		323		112
Foreign currency derivative contract		—		52
Other		749		378
	$	7,248	$	12,857

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

ASU 2016-02

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Schedule of adjustments of topic 842

The following adjustments were recorded in the Company’s balance sheet on January 1, 2019 (in thousands):


	December 31,		Adjustments		January 1,
	2018		Due to Topic 842		2019
Right-of-use assets	$	—	$	5,810	$	5,810
Current portion of operating lease liability	$	—	$	1,892	$	1,892
Operating lease liability, net of current portion	$	—	$	4,684	$	4,684
Accrued expenses and other current liabilities	$	12,857	$	(184)	$	12,673
Other long-term liabilities	$	582	$	(582)	$	—


	December 31, 2019
	As Reported under Topic 842		Under Topic 840		Effect of Change
Right-of-use assets	$	3,970	$	—	$	3,970
Current portion of operating lease liability	$	2,608	$	—	$	2,608
Operating lease liability, net of current portion	$	2,076	$	—	$	2,076
Accrued expenses and other current liabilities	$	7,248	$	7,571	$	(323)
Other long-term liabilities	$	—	$	258	$	(258)


	Year Ended December 31, 2019
	As Reported under Topic 842		Under Topic 840		Effect of Change
Operating expenses:
Research and development related to leases	$	2,070	$	1,962	$	108
General and administrative related to leases		522		498		24
Total	$	2,592	$	2,460	$	132

Property and Equipment

12 Months Ended

Dec. 31, 2019

Property and Equipment

Property and Equipment

10. PROPERTY AND EQUIPMENT

Property and equipment consist of the following:


	December 31,
	2019		2018
	(in thousands)
Laboratory equipment	$	7,243	$	6,965
Office equipment and furniture		870		889
Leasehold improvements		7,949		7,949
Property and equipment, gross		16,062		15,803
Less: accumulated depreciation		(12,626)		(10,192)
Total property and equipment, net	$	3,436	$	5,611

Depreciation expense totaled $2.5 million, $2.7 million and $2.6 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Net Loss Per Share

12 Months Ended

Dec. 31, 2019

Net Loss Per Share

Net Loss Per Share

16. NET LOSS PER SHARE

Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, less shares subject to repurchase, and excludes any dilutive effects of stock-based awards and warrants. Diluted net loss per common share is computed giving effect to all potential dilutive common shares, including common stock issuable upon exercise of stock options, and unvested restricted common stock and stock units. As the Company had net losses for the years ended December 31, 2019, 2018 and 2017, all potential common shares were determined to be anti-dilutive. The following table sets forth the computation of net loss per common share (in thousands, except share and per share amounts):


	Year Ended December 31,
	2019		2018		2017
Numerator:
Net loss	$	(94,940)	$	(91,298)	$	(64,339)
Denominator:
Weighted average common shares outstanding - basic and diluted		64,478,066		56,219,919		47,435,331
Net loss per share - basic and diluted	$	(1.47)	$	(1.62)	$	(1.36)

For the years ended December 31, 2019, 2018 and 2017, the total numbers of securities that could potentially dilute net income per share in the future that were not considered in the diluted net loss per share calculations because the effect would have been anti-dilutive were as follows:


	Year Ended December 31,
	2019	2018	2017
Options to purchase common stock	7,128,247	5,378,008	3,977,160
Warrants to purchase common stock	2,172,899	2,172,899	2,172,899
Restricted stock units	—	199,135	323,819
Performance-based restricted stock units	867,506	395,791	148,216
ESPP shares issuable	78,761	63,413	60,524
Total	10,247,413	8,209,246	6,682,618

The number of potential common shares that would have been included in diluted income per share had it not been for the anti-dilutive effect caused by the net loss, computed by converting these securities using the treasury stock method during the years ended December 31, 2019, 2018 and 2017, was approximately 1.1 million, 1.0 million and 1.0 million, respectively.

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenue	$ 5,281	$ 2,607	$ 42,000
Cost of revenue	600	466	8,400
Gross profit	4,681	2,141	33,600
Operating expenses:
Research and development	71,677	69,373	75,484
General and administrative	24,267	23,715	23,231
Total operating expenses	95,944	93,088	98,715
Loss from operations	(91,263)	(90,947)	(65,115)
Interest expense	(5,726)	(3,534)
Other income, net	2,352	3,187	1,955
Loss before provision for income taxes	(94,637)	(91,294)	(63,160)
Provision for income taxes	303	4	1,179
Net loss	$ (94,940)	$ (91,298)	$ (64,339)
Net loss per common share, basic and diluted	$ (1.47)	$ (1.62)	$ (1.36)
Shares used in computing net loss per share - basic and diluted	64,478,066	56,219,919	47,435,331
Comprehensive loss:
Net loss	$ (94,940)	$ (91,298)	$ (64,339)
Unrealized gains on available-for-sale securities	58	9	24
Comprehensive loss	(94,882)	(91,289)	(64,315)
Licensing
Revenues:
Total revenue	4,500	2,320	$ 42,000
Collaborative development
Revenues:
Total revenue	459
Other
Revenues:
Total revenue	$ 322	$ 287

Equity Incentive Plans - Summary of Non-Vested RSU Activity (Details) - $ / shares	1 Months Ended			12 Months Ended
	Nov. 30, 2018	Jul. 31, 2018	Jan. 31, 2017	Dec. 31, 2019
Service Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Beginning balance				85,609
Number of Shares, Vested				(85,609)
Weighted-Average Grant Date Fair Value Per Share, Beginning balance				$ 4.70
Weighted-Average Grant Date Fair Value Per Share, Vested				$ 4.70
Performance-Based Restricted Stock Units (PRSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Beginning balance				894,764
Number of Shares, Granted		903,374	161,865
Number of Shares, Vested	(125,895)			0
Number of Shares, Forfeited				(45,007)
Number of Shares, Ending balance				849,757
Weighted-Average Grant Date Fair Value Per Share, Beginning balance				$ 4.30
Weighted-Average Grant Date Fair Value Per Share, Forfeited				4.30
Weighted-Average Grant Date Fair Value Per Share, Ending balance				$ 4.30

Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Balance at beginning of year	$ 23,052	$ 20,734	$ 3,892
Additions (subtractions) based on tax positions related to prior year	755	1,634	16,103
Additions based on tax positions related to current year	731	684	739
Balance at end of year	24,538	23,052	20,734
Unrecognized tax benefits that would affect the effective tax rate if recognized	$ 13,200	$ 9,800	$ 8,600

Collaboration and Licensing Agreements - Additional Information (Details) ¥ in Millions, $ in Millions		1 Months Ended					3 Months Ended							12 Months Ended
	Nov. 02, 2018 USD ($)	Nov. 30, 2019 USD ($) item	Feb. 28, 2019 USD ($)	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 CAD ($)	Dec. 31, 2019 JPY (¥)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2019 USD ($)	Jan. 01, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue							$ 2,250,000	$ 3,013,000	$ 18,000	$ 85,000	$ 172,000	$ 30,000	$ 2,320,000			$ 5,281,000	$ 2,607,000	$ 42,000,000
Current assets							252,062,000			176,371,000						252,062,000	176,371,000
Current liabilities							22,220,000			17,728,000						22,220,000	17,728,000
Unbilled revenue							750,000			5,000,000						750,000	5,000,000
Uncharged license fees										$ 1,000,000							1,000,000
Total payments, including an up-front payment and development and sales milestones to be received																19,200,000
Cost of revenue																600,000	466,000	8,400,000
Licensing
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue																4,500,000	2,320,000	42,000,000
Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue																322,000	287,000
Adjustments \| ASU 2014-09
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current assets							5,000,000									5,000,000
Current liabilities							1,000,000									1,000,000
Kyowa Hakko Kirin
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received					$ 30,000,000
Kyowa Hakko Kirin \| Product supply
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue																300,000	300,000
Kyowa Hakko Kirin \| Adjustments \| ASU 2014-09
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Current assets																				$ 5,000,000
Current liabilities																				$ 1,000,000
Unbilled revenue							0									0
Shanghai Fosun Pharmaceutical Industrial Development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue																3,000,000	0
Upfront payment received				$ 12,000,000
Future development milestones	$ 110,000,000
Threshold percentage of net sales for tiered royalties				20.00%
Shanghai Fosun Pharmaceutical Industrial Development \| Adjustments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue			$ 0
Xuanzhu Hk Biopharmaceutical Limited Or Xuanzhu [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue		$ 1,500,000
License fee recognized		1,500,000
Second milestone payment		750,000
Upfront payment received		$ 750,000
Cost of revenue																0
Xuanzhu Hk Biopharmaceutical Limited Or Xuanzhu [Member] \| Licensing
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue																1,500,000
Astra Zeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Uncharged license fees																			$ 1,000,000
Cost of revenue																600,000	466,000	9,400,000
Cost of revenue, aggregate amount recognized							10,466,000									10,466,000
Cost of revenue, Amount Paid																1,002,000	2,864,000	$ 6,000,000
Payments of uncharged license fees, aggregate amount paid							9,866,000									9,866,000
Remaining balance							65,134,000									65,134,000
Astra Zeneca \| Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payment per termination agreement						$ 75,000,000
Astra Zeneca \| Adjustments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of revenue						$ 1,000,000
Kyowa Kirin Co. Ltd
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of pre-clinical study-ready compounds \| item		2
Number of compounds inhibiting the first undisclosed target \| item		1
Upfront payment recognized		$ 10,000,000
License fee receivable, first installment		$ 5,000,000
Term of payment of license fee, first installment		30 days
License fee receivable, Second instalment		$ 5,000,000
Term of agreement		2 years
Initial transaction price		$ 10,000,000
Revenue																500,000
Transaction price allocated to partially unsatisfied performance obligations							9,500,000									9,500,000
Uncharged license fees							$ 4,500,000									4,500,000
Kyowa Kirin Co. Ltd \| Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of development candidates \| item		1
Number of separate collaborative agreements \| item		1
Development and Commercialization [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue																0	2,300,000
Cost of revenue																0	$ 500,000
Development and Commercialization [Member] \| Kyowa Hakko Kirin
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development milestones																55,000,000
Development milestones Received																5,000,000
Commercialization milestones															¥ 8.5	$ 78,300,000
Development and Commercialization [Member] \| Astra Zeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of royalty revenue (as a percent)						10.00%
Percentage of non royalty revenue (as a percent)						20.00%
Development and Commercialization [Member] \| Knight
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total payments, including an up-front payment and development and sales milestones to be received														$ 25

Collaboration and Licensing Agreements

12 Months Ended

Dec. 31, 2019

Collaboration and Licensing Agreements

Collaboration and Licensing Agreements

13. COLLABORATION AND LICENSING AGREEMENTS

Kyowa Kirin Co., Ltd. (2019 KKC Agreement)

In November 2019, the Company entered into a research collaboration and option agreement with KKC, or the 2019 KKC Agreement, for the research to identify two pre-clinical study-ready compounds that are ready for designation as development compounds, with one compound inhibiting the first undisclosed target, or Program 1, and a second inhibiting the second undisclosed target, or Program 2. Pursuant to the 2019 KKC Agreement, upon completion of the research and designation by the research steering committee of one or more development candidates, or DCs, KKC, has the right to execute one or more separate collaborative agreements relating to the development and commercialization of one or both DCs in certain specified territories.

Under the terms of the 2019 KKC Agreement, KKC agreed to pay the Company a non-refundable, non-creditable upfront fee of $10.0 million, which is payable as follows: the first installment of $5.0 million within 30 days of the Effective Date, and the second installment of $5.0 million on the first anniversary of the Effective Date, unless the 2019 KKC Agreement is earlier terminated by KKC due to material breach by the Company. The term of the 2019 KKC Agreement commenced on November 11, 2019, or the Effective Date, and ends on the earliest of: (a) two years following the Effective Date, or (b) the nomination of a program DC for both programs, (c) or the nomination of one program DC and the decision by the parties to cease research for the other program, (d) or the decision by the parties to cease research for both programs. The Company assessed the 2019 KKC Agreement in accordance with ASC 606 and concluded that the contract’s counterparty, KKC, is a customer. Management also considered the modification guidance prescribed in ASC 606 and concluded that the 2019 KKC Agreement should be accounted for as a separate contract from the 2017 KKC Agreement, as defined and discussed below.

The Company identified various promises in the 2019 KKC Agreement, including the grant of an initial research license, the Program 1 research, the Program 2 research, the right to obtain certain development and commercialization rights with Program 1 in certain territories and the right to obtain development and commercialization rights with Program 2 in certain territories, and participation in a joint steering committee, or JSC, and determined that KKC could not benefit from either of the research programs without the research license and participation in the JSC. As such, the combined license, research programs and participation in the JSC were deemed to be the highest level of goods and services that can be deemed distinct for each of the Program 1 research and Program 2 research. The Company concluded that the options to obtain additional development and commercialization rights that are exercisable by KKC under certain circumstances are not performance obligations of the contract at inception because the option fees reflect the standalone selling price of the options, and therefore, the options are not considered to be material rights.

At the outset of the 2019 KKC Agreement, the Company determined that the initial transaction price is $10.0 million and that revenue associated with the combined performance obligations will be recognized as services are provided using a input method. Since transfer of control occurs over time, in management’s judgment this input method is the best measure of progress towards satisfying the performance obligations and reflects a faithful depiction of the transfer of goods and services. Revenue will be recognized over the Program 1 and Program 2 research periods, which are currently expected to extend through the end of 2021. Management will re-evaluate the estimates related to the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur and adjust the timing of revenue recognition as necessary.

During the year ended December 31, 2019, the Company recognized $0.5 million as revenue under the 2019 KKC Agreement in the statement of operations and comprehensive loss. The aggregate amount of the transaction price allocated to the Company’s partially unsatisfied performance obligations as of December 31, 2019 was $9.5 million, of which $4.5 million is presented in the balance sheet as deferred revenue. As of December 31, 2019, the Company expects to recognize the remaining transaction price allocated to the Company’s partially unsatisfied performance obligations over the remaining research terms, which, as noted above, are currently expected to extend through the end of 2021.

Xuanzhu (HK) Biopharmaceutical Limited, or XuanZhu

In November 2019, the Company entered into a license agreement with XuanZhu, or the XuanZhu Agreement, for a license to certain specific patent and patent applications. The Company assessed these arrangements in accordance with ASC 606 and concluded that the contract counterparty, XuanZhu, is a customer. Under the terms of the XuanZhu Agreement, the Company recognized $1.5 million in license fees when the agreement was executed, of which, $750,000 was received upfront in November 2019 and achievement for the second $750,000 payment was determined to be not materially at risk and probable of achievement and it was included in the transaction price and the amount was not probable of revenue reversal. Based on the Company’s assessment, it identified that it has one combined performance obligation, which is the license and the specific patent grant.

In addition to the license fee of $1.5 million, the Company may be entitled to receive milestone payments. The variable consideration related to the remaining milestone payments has not been included in the transaction price as these were fully constrained at December 31, 2019.

For the year ended December 31, 2019, $1.5 million of license revenue was recorded with no cost of revenue related to the XuanZhu Agreement.

2017 KKC Agreement

In November 2017, the Company entered into an exclusive license agreement with KKC, or the 2017 KKC Agreement, for the development, commercialization and distribution of tenapanor in Japan for cardiorenal indications. The Company granted KKC an exclusive license to develop and commercialize certain NHE3 inhibitors including tenapanor in Japan for the treatment of cardiorenal diseases and conditions, excluding cancer. The Company retained the rights to tenapanor outside of Japan, and also retained the rights to tenapanor in Japan for indications other than those stated above. Pursuant to the License Agreement, KKC is responsible for all of the development and commercialization costs for tenapanor in treatment of cardiorenal diseases and conditions, excluding cancer in Japan. Under the 2017 KKC Agreement, the Company is responsible for supplying the tenapanor drug product for KKC’s use in development and during commercialization until KKC has assumed such responsibility. Additionally, the Company is responsible for supplying the tenapanor drug substance for KKC’s use in development and commercialization throughout the term of the 2017 KKC Agreement, provided that KKC may exercise an option to manufacture the tenapanor drug substance under certain conditions

The Company assessed these arrangements in accordance with ASC 606 and concluded that the contract counterparty, KKC, is a customer. Under the terms of the 2017 KKC Agreement, the Company received $30.0 million in up-front license fees which was recognized as revenue when the agreement was executed. Based on the Company’s assessment, it identified that the license and the manufacturing supply services were its material performance obligations at the inception of the agreement, and as such each of the performance obligations are distinct. Additionally, on January 1, 2018, the Company recorded unbilled revenue under current assets of $5.0 million and an increase in uncharged license fees under current liabilities of $1.0 million related to the first milestone under the 2017 KKC Agreement that KKC achieved in February 2019, reflecting revenues and cost of revenue, respectively, that would have been recognized in the fourth quarter 2017 if the Company had adopted ASC 606 prior to January 1, 2018. On KKC’s achievement of the milestone in February 2019, the balance related to unbilled revenue was adjusted to zero. Correspondingly, the $1.0 million balance related to uncharged license fees that the Company owed to AstraZeneca was reclassified to accounts payable during the first quarter of 2019, and subsequently paid to AstraZeneca during the second quarter of 2019.

In addition to the up-front license fee received of $30.0 million, the Company may be entitled to receive up to $55.0 million in total development milestones, of which $5.0 million has been received to date and 8.5 billion yen in commercialization milestones, or $78.3 million at the currency exchange rate on December 31, 2019, as well as reimbursement of cost, plus a reasonable overhead for the supply of product and high-teen royalties on net sales throughout the term of the agreement. The variable consideration related to the remaining development milestone payments has not been included in the transaction price as these were fully constrained at December 31, 2019.

For the years ended December 31, 2019 and 2018, $0.3 million each of other revenue was recorded for manufacturing supply of tenapanor and other materials to KKC for its product development and clinical trials in Japan, in accordance with the Company’s agreement with KKC, and for each period, negligible cost of revenue was recorded pursuant to the AstraZeneca Termination Agreement.

Shanghai Fosun Pharmaceutical Industrial Development Co. Ltd., or Fosun Pharma

In December 2017, the Company entered into an exclusive license agreement with Fosun Pharma, or the Fosun Agreement, for the development, commercialization and distribution of tenapanor in China for both hyperphosphatemia and irritable bowel syndrome with constipation, or IBS-C. The Company assessed these arrangements in accordance with ASC 606 and concluded that the contract counterparty, Fosun Pharma, is a customer. Under the terms of the Fosun Agreement, the Company received $12.0 million in up-front license fees which was recognized as revenue when the agreement was executed. Based on the Company’s assessment, it identified that the license and the manufacturing supply services were its material performance obligations at the inception of the agreement, and as such each of the performance obligations are distinct.

In addition, the Company may be entitled to additional development and commercialization milestones of up to $110.0 million, as well as reimbursement of cost plus a reasonable overhead for the supply of product and tiered royalties on net sales ranging from the mid-teens to 20%. The variable consideration related to the remaining development milestone payments has not been included in the transaction price as these were fully constrained at December 31, 2019.

For the year ended December 31, 2019, $3.0 million revenue was recorded towards achievement of a milestone related to the Fosun Agreement, and for the year ended December 31, 2018, there was no revenue recorded.

Knight Therapeutics, Inc., or Knight

In March 2018, the Company entered into an exclusive license agreement with Knight Therapeutics, Inc., or the Knight Agreement, for the development, commercialization and distribution of tenapanor in Canada for hyperphosphatemia and IBS-C. The Company assessed these arrangements in accordance with ASC 606 and concluded that the contract counterparty, Knight, is a customer. Based on the Company’s assessment, it identified that the license and the manufacturing supply services were its material performance obligations at the inception of the agreement, and as such each of the performance obligations are distinct.

Under the terms of the agreement, the Company is eligible to receive up to CAD 25 million in total payments, or $19.2 million at the currency exchange rate on December 31, 2019, including an up-front payment and development and sales milestones, reimbursement of supply costs on a schedule specifying cost per tablet, with a reasonable mark up for overhead, as well as tiered royalty rates on net sales ranging from the mid-single digits to the low twenties. The variable consideration related to the remaining development milestone payments has not been included in the transaction price as these were fully constrained at December 31, 2019.

For the years ended December 31, 2019 and 2018, zero and $2.3 million of revenue was recorded, respectively, related to the Knight Agreement, and zero and $0.5 million of cost of revenue was recorded, respectively, pursuant to the AstraZeneca Termination Agreement.

AstraZeneca

In June 2015, the Company entered into a termination agreement with AstraZeneca, or the AstraZeneca Termination Agreement, pursuant to which the Company remains liable to pay AstraZeneca license fees for (i) future royalties at a royalty rate of 10% of net sales of tenapanor or other NHE3 products by the Company or its licensees, and (ii) 20% of non-royalty revenue received from a new collaboration partner should the Company elect to license, or otherwise provide rights to develop and commercialize tenapanor or certain other NHE3 inhibitors, up to a maximum of $75.0 million in aggregate for (i) and (ii). To date in aggregate, the Company has recognized $10.5 million of the $75.0 million, recorded as cost of revenue, as follows:


	Cost of Revenue
	Recognized			Amount Paid
	(in thousands)
Year 2017	$	9,400	*	$	6,000
Year 2018		466			2,864
Year 2019		600			1,002
Total	$	10,466		$	9,866
Maximum payment per termination agreement					75,000
Remaining potential commitment				$	65,134

_______________________

* Includes the $1,000 adjustment recorded pursuant to the adoption of ASC 606, as discussed in Note 2.

Equity Incentive Plans - Employee Stock Purchase Plan (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Beginning balance	608,528
Shares Available for Grant, Shares authorized	2,490,417
Shares Available for Grant, Ending balance	1,196,746
Options Issued and Outstanding Number of Shares, Beginning balance	5,506,760
Options Issued and Outstanding Number of Shares, Ending balance	7,272,768
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Beginning balance	680,322
Shares Available of Grant, Shares purchased	(160,744)
Shares Available for Grant, Ending balance	519,578
Options Issued and Outstanding Number of Shares, Beginning balance	330,936
Number of shares issued under ESPP	160,744
Options Issued and Outstanding Number of Shares, Ending balance	491,680
Purchase Price per Share \| $ / shares	$ 2.48
Gross Proceeds \| $	$ 396

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Measurements

Summary of Fair Value Measurements of Company's Financial Assets and Liabilities

The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy (in thousands):


	December 31, 2019
	Total Fair Value		Level 1		Level 2		Level 3
Assets:
Money market funds	$	147,208	$	147,208	$	—	$	—
Corporate bonds		33,134		—		33,134		—
Commercial paper		56,041		—		56,041		—
Asset-backed securities		8,005		—		8,005		—
Total	$	244,388	$	147,208	$	97,180	$	—

Liabilities:
Derivative liability for Exit Fee	$	969	$	—	$	—	$	969
Total	$	969	$	—	$	—	$	969


	December 31, 2018
	Total Fair Value		Level 1		Level 2		Level 3
Assets:
Money market funds	$	73,238	$	73,238	$	—	$	—
U.S. treasury securities		3,996		3,996		—		—
Corporate bonds		34,590		—		34,590		—
Commercial paper		43,154		—		43,154		—
Asset-backed securities		9,378		—		9,378		—
Total	$	164,356	$	77,234	$	87,122	$	—

Liabilities:
Derivative liability for exit fee	$	533	$	—	$	—	$	533
Foreign currency derivative contracts		52		—		52		—
Total	$	585	$	—	$	52	$	533

Summary of Changes in the Fair Value of Recurring Measurements

Changes in the fair value of recurring measurements included in Level 3 of the fair value hierarchy are presented as other income (expense), net in the Company's statements of operations and were as follows for the year ended December 31, 2019 (in thousands):


	Estimated Fair Value
	of Derivative Liability
Balance of Level 3 Liabilities at December 31, 2017	$	—
Initial estimated fair value of derivative liability for Exit Fee in May 2018		546
Change in estimated fair value of derivative liability for Exit Fee		(13)
Balance of Level 3 Liabilities at December 31, 2018		533
Change in estimated fair value of derivative liability for Exit Fee		436
Balance of Level 3 Liabilities at December 31, 2019	$	969

Cash, Cash Equivalents and Short-Term Investments

12 Months Ended

Dec. 31, 2019

Cash, Cash Equivalents and Short-Term Investments

Cash, Cash Equivalents and Short-Term Investments

3. CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS

Securities classified as cash, cash equivalents and short-term investments as of December 31, 2019 and December 31, 2018 are summarized below (in thousands). Estimated fair value is based on quoted market prices for these investments.


	December 31, 2019
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,124	$	—	$	—	$	3,124
Money market funds		147,208		—		—		147,208
Corporate bonds		11,441		—		—		11,441
Commercial paper		19,357		3		—		19,360
Total cash and cash equivalents	$	181,130	$	3	$	—	$	181,133
Short-term investments
Corporate bonds	$	21,690	$	6	$	(3)	$	21,693
Commercial paper		36,667		14		—		36,681
Asset-backed securities		8,005		—		—		8,005
Total short-term investments	$	66,362	$	20	$	(3)	$	66,379
Total cash equivalents and investments	$	247,492	$	23	$	(3)	$	247,512


	December 31, 2018
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,733	$	—	$	—	$	3,733
Money market funds		73,238		—		—		73,238
Commercial paper		1,797		—		—		1,797
Total cash and cash equivalents	$	78,768	$	—	$	—	$	78,768
Short-term investments
U.S. treasury securities	$	3,996	$	—	$	—	$	3,996
Corporate bonds		34,611		—		(21)		34,590
Commercial paper		41,371		—		(14)		41,357
Asset-backed securities		9,381		—		(3)		9,378
Total short-term investments	$	89,359	$	—	$	(38)	$	89,321
Total cash equivalents and investments	$	168,127	$	—	$	(38)	$	168,089

Cash equivalents consist of money market funds and other debt securities with original maturities of three months or less at the time of purchase, and the carrying amount is a reasonable approximation of fair value. The Company invests its cash in high quality securities of financial and commercial institutions. These securities are carried at fair value, which is based on readily available market information, with unrealized gains and losses included in accumulated other comprehensive income (loss) within stockholders’ equity on the Company’s balance sheets. The Company uses the specific identification method to determine the amount of realized gains or losses on sales of marketable securities. Realized gains or losses have been insignificant and are included in other income (expense), net, in the statement of operations.

All available-for-sale securities held as of December 31, 2019 and 2018, had contractual maturities of less than one year. The Company’s available-for-sale securities are subject to a periodic impairment review. The Company considers a debt security to be impaired when its fair value is less than its carrying cost, in which case the Company would further review the investment to determine whether it is other-than-temporarily impaired. When the Company evaluates an investment for other-than-temporary impairment, the Company reviews factors such as the length of time and extent to which fair value has been below cost basis, the financial condition of the issuer and any changes thereto, intent to sell, and whether it is more likely than not the Company will be required to sell the investment before the recovery of its cost basis. If an investment is other-than-temporarily impaired, the Company writes it down through the statement of operations to its fair value and establishes that value as a new cost basis for the investment. The Company did not identify any of its available-for-sale securities as other-than-temporarily impaired in any of the periods presented. As of December 31, 2019 and 2018, no investment was in a continuous unrealized loss position for more than one year and the Company believes that it is more likely than not that the investments will be held until maturity or a forecasted recovery of fair value.

Derivative Financial Instruments	12 Months Ended
Derivative Financial Instruments	Dec. 31, 2019
Derivative Financial Instruments
Derivative Financial Instruments	5. DERIVATIVE FINANCIAL INSTRUMENTS Foreign Currency Exchange Rate Exposure The Company has used forward foreign currency exchange contracts to secure a foreign currency exchange rate when a contract is executed involving payment in a foreign currency in order to minimize cash flow exposure to fluctuating exchange rates. Such exposure results from portions of the Company’s forecasted cash outflows being denominated in currencies other than the U.S. dollar, primarily the Swiss franc, or CHF, and the euro, or EUR. The derivative instruments the Company uses to hedge this exposure are not designated as cash flow hedges, and as a result, changes in the fair value of the derivative instruments are recorded in other income (expense), net, in the Company's statements of operations and comprehensive loss. The fair values of forward foreign currency exchange contracts are estimated using current exchange rates and interest rates and take into consideration the current creditworthiness of the counterparties. In March 2019, the Company settled its forward foreign currency exchange contract in the aggregate notional amount of CHF 3.3 million. As of December 31, 2019, the Company has no open forward foreign currency exchange contracts. The net loss associated with the Company's derivative instruments of $60,558 and $124,194 for the years ended December 31, 2019 and 2018, respectively, is recognized in other income (expense), net, in the statement of operations and comprehensive loss. There were no expenses related to the Company’s derivative instruments during the year ended December 31, 2017.

Equity Incentive Plans - Summary of Weighted-Average Assumptions to Estimate Fair value of Stock Option Awards and Employee Stock Purchase Plan (Details)	12 Months Ended
	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years
Volatility	81.00%
Risk-free interest rate	2.42%
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 months
Volatility	69.00%
Risk-free interest rate	2.20%

Summary of Significant Accounting Policies - Operating expense (Details) - ASU 2016-02 $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	$ 2,592
Under Topic 840
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	2,460
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	132
Research and development
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	2,070
Research and development \| Under Topic 840
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	1,962
Research and development \| Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	108
General and administrative
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	522
General and administrative \| Under Topic 840
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	498
General and administrative \| Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease expense	$ 24

Borrowings (Tables)

12 Months Ended

Dec. 31, 2019

Borrowings

Schedule of Future Debt Payment Obligations

As of December 31, 2019, the Company’s future debt payment obligations towards the principal and final fee, excluding interest payments and the Exit Fee are as follows (in thousands):


2020	$	2,083
2021		25,000
2022		24,892
Total principal and final fee payments		51,975
Less: Unamortized discount and debt issuance costs		(741)
Less: Unaccreted value of final fee		(1,220)
Loan payable		50,014
Less: Loan payable, current portion		1,183
Loan payable, net of current portion	$	48,831

Equity Incentive Plans - Summary of Activity Under 2008 Plan, 2014 Plan and Inducement Plan Including Grants to Nonemployees Issued (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity Incentive Plans
Shares Available for Grant, Beginning balance	608,528
Shares Available for Grant, Options authorized	2,490,417
Shares Available for Grant, Options granted	(2,362,685)
Shares Available for Grant, Options exercised	0
Shares Available for Grant, Options canceled	528,615
Issuance of common stock for services and restricted stock units, net of forfeitures	(45,007)
Shares Available for Grant, Issuance of common stock for services	(113,136)	(75,183)	(46,858)
Shares Available for Grant, Ending balance	1,196,746	608,528
Options Issued and Outstanding Number of Shares, Beginning balance	5,506,760
Options Issued and Outstanding Number of Shares, Options authorized	0
Options Issued and Outstanding Number of Shares, Options granted	2,362,685
Options Issued and Outstanding Number of Shares, Options exercised	(68,062)
Options Issued and Outstanding Number, Options canceled	(528,615)
Options Issued and Outstanding Number of Shares, Issuance of common stock for services	0
Options Issued and Outstanding Number of Shares, Ending balance	7,272,768	5,506,760
Options Issued and Outstanding Average Exercise Price per Share, Beginning balance	$ 8.32
Options Issued and Outstanding Number of Shares, Expected to vest	6,754,711
Options Issued and Outstanding Number of Shares, Exercisable	4,183,281
Options Issued and Outstanding Average Exercise Price per Share, Options granted	$ 2.56
Options Issued and Outstanding Average Exercise Price per Share, Options exercised	2.59
Options Issued and Outstanding Average Exercise Price per Share, Options canceled	7.69
Options Issued and Outstanding Average Exercise Price per Share, Issuance of common stock for services	0
Options Issued and Outstanding Average Exercise Price per Share, Ending balance	6.55	$ 8.32
Options Issued and Outstanding Average Exercise Price per Share, Expected to vest	6.74
Options Issued and Outstanding Average Exercise Price per Share, Exercisable	$ 7.95
Weighted Average Remaining Contractual Term, Ending Balance	7 years 4 months 24 days
Weighted Average Remaining Contractual Term, Vested and Expected to Vest	7 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 5 months 16 days
Aggregate Intrinsic Value, Ending balance	$ 19,128
Aggregate Intrinsic Value, Expected to Vest	17,217
Aggregate Intrinsic Value, Exercisable	$ 8,753

Cash, Cash Equivalents and Short-Term Investments (Tables)

12 Months Ended

Dec. 31, 2019

Cash, Cash Equivalents and Short-Term Investments

Schedule of Securities Classified as Cash, Cash Equivalents and Short-Term Investments


	December 31, 2019
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,124	$	—	$	—	$	3,124
Money market funds		147,208		—		—		147,208
Corporate bonds		11,441		—		—		11,441
Commercial paper		19,357		3		—		19,360
Total cash and cash equivalents	$	181,130	$	3	$	—	$	181,133
Short-term investments
Corporate bonds	$	21,690	$	6	$	(3)	$	21,693
Commercial paper		36,667		14		—		36,681
Asset-backed securities		8,005		—		—		8,005
Total short-term investments	$	66,362	$	20	$	(3)	$	66,379
Total cash equivalents and investments	$	247,492	$	23	$	(3)	$	247,512


	December 31, 2018
			Gross Unrealized
	Amortized Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,733	$	—	$	—	$	3,733
Money market funds		73,238		—		—		73,238
Commercial paper		1,797		—		—		1,797
Total cash and cash equivalents	$	78,768	$	—	$	—	$	78,768
Short-term investments
U.S. treasury securities	$	3,996	$	—	$	—	$	3,996
Corporate bonds		34,611		—		(21)		34,590
Commercial paper		41,371		—		(14)		41,357
Asset-backed securities		9,381		—		(3)		9,378
Total short-term investments	$	89,359	$	—	$	(38)	$	89,321
Total cash equivalents and investments	$	168,127	$	—	$	(38)	$	168,089

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (94,940)	$ (91,298)	$ (64,339)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	2,501	2,678	2,639
Amortization of deferred financing costs	670	236	375
Amortization of deferred compensation for services	309	253	192
Amortization of (premium) discount on investment securities	(698)	(1,136)	11
Non-cash lease expense	1,839
Stock-based compensation	9,936	9,226	9,590
Change in derivative liabilities	436	111
Non-cash interest associated with debt discount accretion	478	303
Changes in operating assets and liabilities:
Unbilled revenue	4,250
Accounts receivable	85	10,711	(10,796)
Prepaid expenses and other assets	93	525	(2,148)
Accounts payable	39	(2,730)	(1,027)
Accrued compensation and benefits	1,730	(506)	68
Lease liabilities	(1,892)
Accrued and other liabilities	(5,861)	1,353	245
Deferred revenue	4,541
Net cash used in operating activities	(76,484)	(70,274)	(65,190)
Investing activities
Proceeds from maturities of investments	124,369	138,600	133,701
Sales and redemptions of investments	2,000	850	17,957
Purchases of investments	(102,671)	(169,033)	(84,013)
Purchases of property and equipment	(325)	(311)	(2,355)
Net cash provided by (used in) investing activities	23,373	(29,894)	65,290
Financing activities
Proceeds from underwritten public offering, net of issuance costs	134,927	53,770
Proceeds from issuance of common stock upon private placement, net of issuance costs	19,975
Proceeds from issuance of common stock under stock plans	396	491	623
Issuance of common stock upon exercise of options	178		62
Proceeds from loan payable, net of issuance costs		49,292
Net cash provided by financing activities	155,476	103,553	685
Net increase in cash and cash equivalents	102,365	3,385	785
Cash and cash equivalents at beginning of period	78,768	75,383	74,598
Cash and cash equivalents at end of period	181,133	78,768	75,383
Supplementary disclosure of cash flow information:
Income taxes paid	2	4	3
Supplementary disclosure of non-cash activities:
Right-of-use assets obtained in exchange for lease obligations	5,810
Issuance of common stock for services	$ 312	303	201
Issuance of derivative in connection with issuance of loan payable		$ 546
Acquisition of property and equipment included in accounts payable and accrued liabilities			$ 55

Summary of Significant Accounting Policies - Prior Period Errors (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Research and Development Expense	$ 71,677	$ 69,373	$ 75,484
Accrued Liabilities and Other Liabilities	7,248	12,857
Effect of Change
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued Liabilities and Other Liabilities	(323)
Overstatement due to clinical trial accrual errors \| Effect of Change
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Research and Development Expense		3,600
Accrued Liabilities and Other Liabilities	$ 3,600	$ 3,600

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Accrued Expenses and Other Current Liabilities

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consist of the following (in thousands):


	December 31,		December 31,
	2019		2018
Accrued clinical and non-clinical expenses	$	3,451	$	9,790
Accrued contract manufacturing expenses		1,414		1,971
Derivative liability for exit fee		969		533
Accrued regulatory expenses		342		21
Accrued professional and consulting services		323		112
Foreign currency derivative contract		—		52
Other		749		378
	$	7,248	$	12,857

Summary of Significant Accounting Policies - Liquidity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Cash and cash equivalents and short-term investments	$ 247,492	$ 168,127
Proceeds from issuance initial public offering	134,900
Net proceeds from private placement	$ 19,975

Net Loss Per Share - Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share attributable to common stockholders	10,247,413	8,209,246	6,682,618
Potential common shares that would have been included in diluted income per share were not anti-dilutive effect caused by the net loss, computed by converting these securities using the treasury stock method	1,100,000	1,000,000	1,000,000
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share attributable to common stockholders	7,128,247	5,378,008	3,977,160
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share attributable to common stockholders	2,172,899	2,172,899	2,172,899
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share attributable to common stockholders		199,135	323,819
Performance-Based Restricted Stock Units (PRSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share attributable to common stockholders	867,506	395,791	148,216
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share attributable to common stockholders	78,761	63,413	60,524

Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 16,062	$ 15,803
Less: accumulated depreciation	(12,626)	(10,192)
Total property and equipment, net	3,436	5,611
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,243	6,965
Office Equipment And Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	870	889
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,949	$ 7,949

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2019

Net Loss Per Share

Computation of Basic and Diluted Loss Per Share Attributable to Common Stockholders

The following table sets forth the computation of net loss per common share (in thousands, except share and per share amounts):


	Year Ended December 31,
	2019		2018		2017
Numerator:
Net loss	$	(94,940)	$	(91,298)	$	(64,339)
Denominator:
Weighted average common shares outstanding - basic and diluted		64,478,066		56,219,919		47,435,331
Net loss per share - basic and diluted	$	(1.47)	$	(1.62)	$	(1.36)

Calculation of Anti-Dilutive Potentially Dilutive Securities Not Included in Diluted Per Share


	Year Ended December 31,
	2019	2018	2017
Options to purchase common stock	7,128,247	5,378,008	3,977,160
Warrants to purchase common stock	2,172,899	2,172,899	2,172,899
Restricted stock units	—	199,135	323,819
Performance-based restricted stock units	867,506	395,791	148,216
ESPP shares issuable	78,761	63,413	60,524
Total	10,247,413	8,209,246	6,682,618

Fair Value Measurements - Loan and Security Agreement (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2018	Dec. 31, 2019
Fair Value Measurements
Exit Fee	$ 1.5
Solar Capital and Western Alliance Bank Loan Agreement [Member] \| Level 3 [Member]
Fair Value Measurements
Potential payment to Solar Capital Ltd. and Western Alliance Bank		$ 1.5
Percentage of increase in risk component		10.00%
Percentage decrease in risk component		10.00%
Fair value fluctuation due to increase in risk component		$ 0.1
Fair value fluctuation due to decrease in risk component		$ 0.1

Equity Incentive Plans - Summary of Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expenses	$ 9,936	$ 9,226	$ 9,590
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expenses	4,104	3,666	4,585
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expenses	$ 5,832	$ 5,560	$ 5,005

Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Measurements

Fair Value Measurements

4. FAIR VALUE MEASUREMENTS

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs.

The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows:

Level 1 – Valuations are based on quoted prices in active markets for identical assets or liabilities and readily accessible by the Company at the reporting date. Examples of assets and liabilities utilizing Level 1 inputs are certain money market funds, U.S. treasuries and trading securities with quoted prices on active markets.

Level 2 – Valuations based on inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Examples of assets and liabilities utilizing Level 2 inputs are corporate bonds, commercial paper, certificates of deposit and over-the-counter derivatives.

Level 3 – Valuations based on unobservable inputs in which there is little or no market data, which require the Company to develop its own assumptions.

The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy (in thousands):


	December 31, 2019
	Total Fair Value		Level 1		Level 2		Level 3
Assets:
Money market funds	$	147,208	$	147,208	$	—	$	—
Corporate bonds		33,134		—		33,134		—
Commercial paper		56,041		—		56,041		—
Asset-backed securities		8,005		—		8,005		—
Total	$	244,388	$	147,208	$	97,180	$	—

Liabilities:
Derivative liability for Exit Fee	$	969	$	—	$	—	$	969
Total	$	969	$	—	$	—	$	969


	December 31, 2018
	Total Fair Value		Level 1		Level 2		Level 3
Assets:
Money market funds	$	73,238	$	73,238	$	—	$	—
U.S. treasury securities		3,996		3,996		—		—
Corporate bonds		34,590		—		34,590		—
Commercial paper		43,154		—		43,154		—
Asset-backed securities		9,378		—		9,378		—
Total	$	164,356	$	77,234	$	87,122	$	—

Liabilities:
Derivative liability for exit fee	$	533	$	—	$	—	$	533
Foreign currency derivative contracts		52		—		52		—
Total	$	585	$	—	$	52	$	533

Where quoted prices are available in an active market, securities are classified as Level 1. The Company classifies money market funds, U.S. treasury securities and U.S. treasury notes as Level 1. When quoted market prices are not available for the specific security, the Company estimates fair value by using benchmark yields, reported trades, broker/dealer quotes and issuer spreads. The Company classifies corporate bonds, commercial paper, asset-backed securities and foreign currency derivative contracts as Level 2. In certain cases, where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3. There were no transfers between Level 1 and Level 2 during the periods presented.

In May 2018, in connection with entering into the Loan Agreement, as defined and discussed in Note 6, the Company entered into an agreement pursuant to which the Company agreed to pay $1.5 million in cash, or the Exit Fee, upon any change of control transaction in respect of the Company or if the Company obtains both (i) FDA approval of tenapanor for the treatment of hyperphosphatemia in CKD patients on dialysis and (ii) FDA approval of tenapanor for the treatment of patients with irritable bowel syndrome with constipation, or IBS-C, which was obtained on September 12, 2019 when the FDA approved IBSRELA® (tenapanor), a 50 mg, twice daily oral pill for the treatment of IBS-C, in adults (the “Exit Fee Agreement”). Notwithstanding the prepayment or termination of the Term Loan, the Company’s obligation to pay the Exit Fee will expire on May 16, 2028. The Company concluded that the Exit Fee is a freestanding derivative which should be accounted for at fair value on a recurring basis. The estimated fair value of the Exit Fee is recorded as a derivative liability and included in accrued expense and other current liabilities on the accompanying balance sheets.

The fair value of the derivative liability was determined using a discounted cash flow analysis and is classified as a Level 3 measurement within the fair value hierarchy since the Company’s valuation utilized significant unobservable inputs. Specifically, the key assumptions included in the calculation of the estimated fair value of the derivative instrument include: i) the Company’s estimates of both the probability and timing of a potential $1.5 million payment to Solar Capital Ltd. and Western Alliance Bank as a result of the FDA approvals, and ii) a discount rate which was derived from the Company's estimated cost of debt, adjusted with current LIBOR. Generally, increases or decreases in the probability of occurrence would result in a directionally similar impact in the fair value measurement of the derivative instrument and it is estimated that a 10% increase (decrease) in the probability of occurrence would result in a fair value fluctuation of approximately $0.1 million.


	Estimated Fair Value
	of Derivative Liability
Balance of Level 3 Liabilities at December 31, 2017	$	—
Initial estimated fair value of derivative liability for Exit Fee in May 2018		546
Change in estimated fair value of derivative liability for Exit Fee		(13)
Balance of Level 3 Liabilities at December 31, 2018		533
Change in estimated fair value of derivative liability for Exit Fee		436
Balance of Level 3 Liabilities at December 31, 2019	$	969

The carrying amounts reflected in the balance sheets for cash equivalents, short-term investments, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values at both December 31, 2019 and December 31, 2018, due to their short-term nature.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Line Items]

Summary of Undiscounted Cash Payment Obligations for Operating Lease Liabilities

The following table summarizes the Company’s undiscounted cash payment obligations for its operating lease liabilities as of December 30, 2019 (in thousands):


Years Ending December 31,
2020	$	3,065
2021		2,183
Total undiscounted operating lease payments		5,248
Imputed interest expenses		(564)
Total operating lease liabilities		4,684
Less: Current portion of operating lease liability		2,608
Operating lease liability, net of current portion	$	2,076

Operating Equipment Leases

Property, Plant and Equipment [Line Items]

Summary of Undiscounted Cash Payment Obligations for Operating Lease Liabilities

Future minimum payments on the Company’s noncancelable operating leases as of December 31, 2019 are as follows (in thousands):


Year Ended December 31,	Amounts
2020	$	3,121
2021		2,213
Total	$	5,334

Leases - Balance Sheet and Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Additional details of the leases
Right-of-use assets	$ 3,970
Current portion of lease liabilities	2,608
Operating lease liability, net of current portion	2,076
Total liabilities	$ 4,684
Weighted-average remaining life	1 year 9 months 18 days
Weighted-average discount rate	12.99%
Facilities
Operating lease cost	$ 2,592	$ 1,800	$ 1,700
Cash paid for operating lease	$ 2,645

Warrants (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Warrant [Abstract]
Warrants sold and issued	7,242,992
Common stock to be issued if warrants are exercised (in shares)	2,172,899
Gross proceeds	$ 77.8
Net proceeds	$ 74.3
Purchase price of common shares	$ 10.70
Purchase price of warrants	0.125
Exercise price for warrants	$ 13.91	$ 13.91
Warrant exercise period	5 years
Maximum beneficial ownership percentage	9.99%
Warrants exercised		0	0	0

Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2019

Summary of Activity Under 2008 Plan, 2014 Plan and Inducement Plan Including Grants to Nonemployees Issued


		Options Issued and Outstanding			Weighted
			Weighted-Average		Average
	Shares Available		Exercise Price per		Remaining	Aggregate
	for Grant	Number of Shares	Share		Contractual Term	Intrinsic Value
					(in Years)	(in thousands)
Balance at December 31, 2018	608,528	5,506,760	$	8.32
Options authorized	2,490,417	—	$	—
Options granted	(2,362,685)	2,362,685	$	2.56
Options exercised	—	(68,062)	$	2.59
Options canceled	528,615	(528,615)	$	7.69
Issuance of common stock for services	(113,136)	—		—
Forfeitures of PRSUs granted in prior years	45,007	—		—
Balance at December 31, 2019	1,196,746	7,272,768	$	6.55	7.40	$	19,128
Vested and expected to vest at December 31, 2019		6,754,711	$	6.74	7.30	$	17,217
Exercisable at December 31, 2019		4,183,281	$	7.95	6.46	$	8,753

Summary of Weighted-Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan


	Year Ended December 31,
	2019
Expected term (years)	6.00
Expected volatility	81	%
Risk-free interest rate	2.42	%
Dividend yield	—	%

Summary of Non-Vested RSU Activity


					Weighted-
		Weighted-Average			Average Grant
	Number of	Grant Date Fair		Number of	Date Fair Value
	RSUs	Value Per Share		PRSUs	Per Share
Non-vested restricted stock units at December 31, 2018	85,609	$	4.70	894,764	$	4.30
Granted	—	$	—	—	$	—
Vested	(85,609)	$	4.70	—	$	—
Forfeited	—	$	—	(45,007)	$	4.30
Non-vested restricted stock units at December 31, 2019	—	$	—	849,757	$	4.30

Summary of Stock-Based Compensation Expense Recognized


	Year Ended December 31,
	2019		2018			2017
	(in thousands)
Research and development	$	4,104	$	3,666	$	4,585
General and administrative		5,832		5,560		5,005
Total	$	9,936	$	9,226	$	9,590

Summary of Stock-Based Compensation Expense Not Yet Recognized



	At December 31, 2019
	Unrecognized Compensation Expense		Average Vesting Period
	(in thousands)		(Years)
Stock options grants	$	8,277	2.5
PRSU grants	$	965	0.7
ESPP	$	53	0.2

2014 Employee Stock Purchase Plan [Member]

Summary of Activity Under 2008 Plan, 2014 Plan and Inducement Plan Including Grants to Nonemployees Issued


	Shares Available	Number of Shares	Purchase Price
	for Grant	Purchased	per Share		Gross Proceeds
					(in thousands)
Balance at December 31, 2018	680,322	330,936
Shares purchased	(160,744)	160,744	$	2.48	$	396
Balance at December 31, 2019	519,578	491,680

Summary of Weighted-Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan


	Year Ended December 31,
	2019
Expected term (years)	0.5
Expected volatility	69	%
Risk-free interest rate	2.20	%
Dividend yield	—	%

Borrowings

12 Months Ended

Dec. 31, 2019

Borrowings

Borrowings

6. BORROWINGS

Solar Capital and Western Alliance Bank Loan Agreement

On May 16, 2018, the Company entered into a loan and security agreement, or the Loan Agreement, with Solar Capital Ltd. and Western Alliance Bank, or collectively the Lenders. The Loan Agreement provides for a $50.0 million term loan facility with a maturity date of November 1, 2022, or the Term Loan. The full amount of the loan was funded on May 16, 2018. The Company received net proceeds from the loan of approximately $49.3 million, after deducting the closing fee, legal expenses and issuance costs.

Borrowings under the Term Loan bear interest at a floating per annum rate equal to 7.45% plus the one-month London Inter-bank Offered Rate, or LIBOR. The Company is permitted to make interest-only payments on the Term Loan through June 1, 2020, unless the Company achieves its primary endpoint in the Phase 3 study of tenapanor for the treatment of hyperphosphatemia in end-stage renal disease patients on dialysis, prior to June 1, 2020, in which case the Company is permitted to make interest-only payments on the Term Loan through December 1, 2020. On December 3, 2019, the Company reported positive topline results for PHREEDOM, a long-term Phase 3 study evaluating the efficacy and safety of tenapanor as monotherapy for the treatment of hyperphosphatemia in patients with CKD on dialysis. The Lenders are in agreement that these positive data from the Phase 3 PHREEDOM study achieve the “Phase 3 Endpoint” required by the Loan Agreement to extend the interest only period by six months to December 1, 2020. Accordingly, beginning on December 1, 2020 through the maturity date, the Company will be required to make monthly payments of interest plus repayment of the Term Loan in consecutive equal monthly installments of principal. The Company paid a closing fee of 1% of the Term Loan, or $0.5 million, upon the closing of the Term Loan. The Company is obligated to pay a final fee equal to 3.95% of the Term Loan upon the earliest to occur of the maturity date, the acceleration of the Term Loan, the prepayment or repayment of the Term Loan or the termination of the Loan Agreement. The Company may voluntarily prepay the outstanding Term Loan, subject to a prepayment premium of (i) 3% of the principal amount of the Term Loan if prepaid prior to or on the first anniversary of the Closing Date, (ii) 2% of the principal amount of the Term Loan if prepaid after the first anniversary of the Closing Date through and including the second anniversary of the Closing Date, or (iii) 1% of the principal amount of the Term Loan if prepaid after the second anniversary of the Closing Date and prior to the maturity date. The Term Loan is secured by substantially all the Company’s assets, except for the Company’s intellectual property and certain other customary exclusions. Additionally, in connection with the Term Loan, the Company entered into the Exit Fee Agreement, as discussed in Note 4.

The Loan Agreement contains customary representations and warranties and customary affirmative and negative covenants. As of December 31, 2019, the Company was in compliance with all of the covenants set forth in the Loan Agreement.

In addition, the Loan Agreement contains customary events of default that entitle the Lender to cause the Company’s indebtedness under the Loan Agreement to become immediately due and payable, and to exercise remedies against the Company and the collateral securing the Term Loan, including its cash. Upon the occurrence and for the duration of an event of default, an additional default interest rate equal to 4.0% per annum will apply to all obligations owed under the Loan Agreement. As of December 31, 2019, to the Company’s knowledge, there were no facts or circumstances in existence that would give rise to an event of default.

As of December 31, 2019, the Company’s future debt payment obligations towards the principal and final fee, excluding interest payments and the Exit Fee are as follows (in thousands):


2020	$	2,083
2021		25,000
2022		24,892
Total principal and final fee payments		51,975
Less: Unamortized discount and debt issuance costs		(741)
Less: Unaccreted value of final fee		(1,220)
Loan payable		50,014
Less: Loan payable, current portion		1,183
Loan payable, net of current portion	$	48,831

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended			36 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Jan. 01, 2018
Summary of significant accounting policies
Cash and cash equivalents original maturity dates	90 days
Short-term investments maturity period description	Short-term investments consist of debt securities classified as available-for-sale and have maturities greater than 90 days, but less than one year, from the date of acquisition.
Provision for doubtful accounts	$ 0	$ 0	$ 0
Impairment loss of long-lived assets				$ 0
Current assets	252,062	176,371		252,062
Accumulated deficit	(460,452)	(365,512)		(460,452)
Unbilled revenue	750	5,000		750
Current liabilities	$ 22,220	17,728		22,220
Uncharged license fees		$ 1,000
Minimum [Member]
Summary of significant accounting policies
Estimated useful lives	3 years
Maximum [Member]
Summary of significant accounting policies
Estimated useful lives	5 years
ASU 2014-09 \| Adjustments
Summary of significant accounting policies
Current assets	$ 5,000			5,000
Current liabilities	1,000			1,000
ASU 2014-09 \| Adjustments \| Kyowa Hakko Kirin
Summary of significant accounting policies
Current assets					$ 5,000
Accumulated deficit					4,000
Unbilled revenue	$ 0			$ 0
Current liabilities					$ 1,000

Income Taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income tax, federal statutory rate	21.00%	21.00%	35.00%
California
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 88.3
Minimum Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	0.1
Federal Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	232.1
Net operating loss carryforwards, Without Expiration	91.4
Federal Tax Authority [Member] \| Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	11.4
State Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	1.8
State Tax Authority [Member] \| Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	7.8
Foreign Tax Authority [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 1.2

Income Taxes - (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes - (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
State	$ 2	$ 4	$ 5
Foreign	301		1,204
Total current	303	4	1,209
Deferred:
Federal			(30)
Total deferred			(30)
Provision for (benefit from) income taxes	$ 303	$ 4	$ 1,179