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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Mar. 08, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	ARDX
Entity Registrant Name	Ardelyx, Inc.
Entity Central Index Key	0001437402
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		47,603,568
Entity Public Float			$ 168,628,611

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 75,383	$ 74,598
Short-term investments	58,593	126,225
Accounts receivable	10,796
Prepaid expenses and other current assets	4,940	3,169
Total current assets	149,712	203,992
Property and equipment, net	8,032	8,991
Other assets	159	148
Total assets	157,903	213,131
Current liabilities:
Accounts payable	3,933	5,635
Accrued compensation and benefits	3,229	3,161
Accrued and other liabilities	10,709	10,405
Total current liabilities	17,871	19,201
Other long-term liabilities	720	779
Total liabilities	18,591	19,980
Commitments and contingencies (Note 13)
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; no shares issued and outstanding as of December 31, 2017 and 2016
Common stock, $0.0001 par value; 300,000,000 shares authorized; 47,534,979 and 47,309,422 shares issued and outstanding as of December 31, 2017 and December 31, 2016, respectively	5	5
Additional paid-in capital	417,568	407,092
Decrease in accumulated deficit	(278,214)	(213,875)
Accumulated other comprehensive loss	(47)	(71)
Total stockholders' equity	139,312	193,151
Total liabilities and stockholders' equity	$ 157,903	$ 213,131

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
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	47,534,979	47,309,422
Common stock, shares outstanding	47,534,979	47,309,422

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Licensing revenue	$ 42,000		$ 21,611
Collaborative development revenue			2,415
Total revenue	42,000		24,026
Cost of revenue	8,400
Gross profit	33,600		24,026
Operating expenses:
Research and development	75,484	$ 94,161	39,885
General and administrative	23,231	18,734	13,530
Total operating expenses	98,715	112,895	53,415
Loss from operations	(65,115)	(112,895)	(29,389)
Other income (expense), net	1,955	508	(261)
Loss before provision for income taxes	(63,160)	(112,387)	(29,650)
Provision for (benefit from) income taxes	1,179		(29)
Net loss	$ (64,339)	$ (112,387)	$ (29,621)
Net loss per common share, basic and diluted	$ (1.36)	$ (2.80)	$ (1.29)
Shares used in computing net loss per share - basic and diluted	47,435,331	40,118,522	22,892,640
Comprehensive Loss:
Net loss	$ (64,339)	$ (112,387)	$ (29,621)
Unrealized loss on available-for-sale securities, net of tax	24	(71)
Comprehensive loss	$ (64,315)	$ (112,458)	$ (29,621)

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Common Stock [Member] Private Placement [Member]	Common Stock [Member] Public Offering [Member]	Common Stock [Member] Private Investment in Public Equity (PIPE) [Member]	Common Stock [Member] Restricted Stock Units (RSUs) [Member]	Common Stock [Member]	Additional Paid-in Capital [Member] Private Placement [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]	Accumulated Deficit [Member]	Other Comprehensive Income (Loss) [Member]	Private Placement [Member]	Public Offering [Member]	Private Investment in Public Equity (PIPE) [Member]	Total
Shares, Outstanding					18,589,245
Issuance of common stock, value	$ 1					$ 74,322						$ 74,323
Balance, amount at Dec. 31, 2014					$ 2				$ 132,547	$ (71,867)					$ 60,682
Shares, Outstanding					25,964,886
Issuance of common stock, shares	7,242,992
Issuance of common stock under employee stock purchase plan ,amount									548						548
Issuance of common stock under employee stock purchase plan , shares					41,580
Exercise of stock options, amount									111						$ 111
Exercise of stock options, shares					77,784										77,784
Issuance of common stock for services, amount									194						$ 194
Issuance of common stock for services, shares					13,285										13,285
Stock-based compensation									2,634						$ 2,634
Other									30						30
Net loss										(29,621)					(29,621)
Balance, amount at Dec. 31, 2015					$ 3				210,386	(101,488)					108,901
Balance, shares at Dec. 31, 2015					25,964,886
Shares, Outstanding					25,964,886
Issuance of common stock, value		$ 1	$ 1				$ 80,836	$ 109,735					$ 80,837	$ 109,736
Shares, Outstanding					47,309,422
Issuance of common stock, shares		8,625,000	12,600,230	5,000
Issuance of common stock under employee stock purchase plan ,amount									576						576
Issuance of common stock under employee stock purchase plan , shares					69,054
Exercise of stock options, amount									55						$ 55
Exercise of stock options, shares					25,134										25,134
Issuance of common stock for services, amount									187						$ 187
Issuance of common stock for services, shares					20,118										20,118
Stock-based compensation									5,317						$ 5,317
Other comprehensive income (loss)											$ (71)				(71)
Net loss										(112,387)					(112,387)
Balance, amount at Dec. 31, 2016					$ 5				407,092	(213,875)	(71)				193,151
Balance, shares at Dec. 31, 2016					47,309,422
Shares, Outstanding					47,309,422
Shares, Outstanding					47,534,979
Issuance of common stock, shares				43,597
Issuance of common stock under employee stock purchase plan ,amount									623						$ 623
Balance, shares at Dec. 31, 2016															47,309,422
Issuance of common stock under employee stock purchase plan , shares					99,343
Exercise of stock options, amount									62						$ 62
Exercise of stock options, shares					35,759										35,759
Issuance of common stock for services, amount									201						$ 201
Issuance of common stock for services, shares					46,858										46,858
Stock-based compensation									9,590						$ 9,590
Other comprehensive income (loss)											24				24
Net loss										(64,339)					(64,339)
Balance, amount at Dec. 31, 2017					$ 5				$ 417,568	$ (278,214)	$ (47)				$ 139,312
Balance, shares at Dec. 31, 2017					47,534,979
Shares, Outstanding					47,534,979

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Private Placement [Member]
Stock issuance costs		$ 3,449
Public Offering [Member]
Stock issuance costs	$ 263
Private Investment in Public Equity (PIPE) [Member]
Stock issuance costs	$ 5,413

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (64,339)	$ (112,387)	$ (29,621)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	2,639	1,295	829
Amortization of deferred financing costs	375	346	351
Amortization of deferred compensation for services	192	194	107
Amortization of premium on investment securities	11	(86)
Stock-based compensation	9,590	5,317	2,634
Loss from disposal of fixed assets			65
Changes in operating assets and liabilities:
Accounts receivable	(10,796)		2,584
Prepaid expenses and other assets	(2,148)	1,562	(4,083)
Accounts payable	(1,027)	2,148	(371)
Accrued compensation and benefits	68	795	718
Accrued and other liabilities	245	8,282	2,000
Deferred revenue			(47,053)
Net cash used in operating activities	(65,190)	(92,534)	(71,840)
Investing activities
Proceeds from maturities of investments	133,701	7,600
Sales and redemptions of investments	17,957
Purchases of investments	(84,013)	(133,810)
Purchases of property and equipment	(2,355)	(4,866)	(3,454)
Net cash provided by (used in) investing activities	65,290	(131,076)	(3,454)
Financing activities
Proceeds from issuance of common stock, net of issuance costs		190,573	74,323
Proceeds from issuance of common stock under stock plans	685	631	659
Other			30
Net cash provided by financing activities	685	191,204	75,012
Net increase (decrease) in cash and cash equivalents	785	(32,406)	(282)
Cash and cash equivalents at beginning of period	74,598	107,004	107,286
Cash and cash equivalents at end of period	75,383	74,598	107,004
Supplementary disclosure of cash flow information:
Income taxes paid	3		69
Supplementary disclosure of non-cash financing information:
Acquisition of property and equipment included in accounts payable and accrued liabilities	55	730
Services settled through the issuance of common stock	$ 201	$ 187	$ 194

Organization and Basis of Presentation	12 Months Ended
Organization and Basis of Presentation	Dec. 31, 2017
Accounting Policies [Abstract]
Organization and Basis of Presentation	1. ORGANIZATION AND BASIS OF PRESENTATION Ardelyx, Inc., or “the Company,” is a specialized biopharmaceutical company focused on developing first-in-class, disruptive medicines for the treatment of renal diseases, which affect both the heart and the kidneys. Tenapanor, a first-in-class inhibitor of NHE3, is being evaluated in a second Phase 3 trial for the treatment of hyperphosphatemia in patients with ESRD who are on dialysis. The Company is also advancing a small molecule potassium secretagogue program, RDX013, for the potential treatment of hyperkalemia as well as tenapanor for the treatment of people with irritable bowel syndrome with constipation, or IBS-C, for which the Company is preparing to submit a New Drug Application (“NDA”) to the United States Food and Drug Administration (“FDA”) in the second half of 2018. The Company operates in only one business segment, which is the development of biopharmaceutical products.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation

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

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of Ardelyx and its wholly-owned subsidiary, Ardelyx Cayman Islands, which was placed into voluntary liquidation in December 2017. Intercompany transactions and balances have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the amounts reported in the consolidated 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 differ from those estimates.

Liquidity

The Company has never been profitable on an annual basis and, as of December 31, 2017, the Company has an accumulated deficit of $278.2 million. The Company has incurred net losses of approximately $64.3 million, $112.4 million and $29.6 million in the years ended December 31, 2017, 2016 and 2015, respectively. The Company expects to continue to incur net operating losses for the foreseeable future, as the Company continues the development of, seeks regulatory approval for, and if approved, begins to commercialize and manufacture tenapanor, either directly by the Company or through one or more of its collaboration partners. The Company will need additional funding to support its future operating activities and adequate funding may not be available to the Company on acceptable terms, or at all. The Company’s failure to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the business, results of operations, and financial condition. The Company will need to generate significant revenues to achieve profitability and may never do so.

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 consolidated 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, 2017 or 2016.

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, generally 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 its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2017, there have been no such 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

Revenue from research activities made under collaboration partnership agreements is recognized as the services are provided and when there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collectability is reasonably assured. Revenue generated from research and licensing agreements typically includes up-front signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments, and royalties on future licensees’ product sales.

For revenue agreements with multiple-element arrangements, such as license and development agreements, the Company allocates revenue to each unit of accounting based on the relative selling price of each unit. When applying the relative selling price method, the Company determines the selling price for each deliverable using vendor-specific objective evidence or third-party evidence. If neither exists, the Company uses its best estimate of selling price for that deliverable. Revenue allocated is then recognized when the four basic revenue recognition criteria are met for each deliverable.

The Company recognizes revenue from upfront payments under license agreements on contract execution if the license payment is a separate unit of accounting and the Company has no continuing performance obligations under the license, as is the case with the Company’s license agreements with KHK and Fosun Pharma. If the license is not a separate unit of accounting, the Company recognizes revenue from upfront payments ratably over the term of its estimated period of performance under the agreement which is recorded as licensing revenue. Reimbursements for development costs incurred under the contract with AstraZeneca, until it was terminated, were classified as collaborative development revenue. The Company recognizes cost reimbursement revenue under collaboration partnership agreements as the related research and development costs for services are rendered. Deferred revenue represents the portion of research or license payments received which has not been earned.

Revenues from milestones, if they are nonrefundable and deemed substantive, are recognized upon successful accomplishment of the milestones. To the extent that non-substantive milestones are achieved and the Company has remaining performance obligations, milestones are deferred and recognized as revenue over the estimated remaining period of performance. The Company will recognize revenue associated with the non-substantive milestones upon achievement of the milestone if there are no undelivered units and it has no remaining performance obligations. The Company will account for sales-based milestones as royalties that will be recognized as revenue upon achievement of the milestone.

Revenue subject to governmental withholding taxes is recognized on a gross basis with the withholding taxes recorded as a component of income tax expense.

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 including 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

As part of the process of preparing our financial statements, the Company is required to estimate its accrued expenses. This process involves reviewing open contracts and purchase orders, communicating with its personnel to identify services that have been performed on its 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 cost. The majority of the Company’s service providers invoice the Company monthly 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 its 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 make adjustments if necessary. Examples of estimated accrued research and development expenses include fees paid to:

contract research organizations (“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 its 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. To date, there have been no material differences from the Company’s estimates to the amounts actually incurred.

Stock-Based Compensation

The Company recognizes compensation expense for all stock-based payment awards made to employees and directors based on estimated fair values. For employee 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, 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.

The Company accounts for equity instruments issued to nonemployees based on their fair values on the measurement dates using the Black-Scholes option-pricing model. The estimated fair values of the options granted to nonemployees are remeasured as they vest. As a result, the noncash charge to operations for nonemployee options with vesting conditions is affected each reporting period by changes in the fair value of the Company’s common stock.

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 under U.S. GAAP 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

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014‑09, Revenue from Contracts with Customers (“ASU 2014‑09”), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014‑09 will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective. In July 2015, the FASB voted to approve a deferral of the effective date of this ASU by one year, and to permit entities to adopt up to one year earlier if they choose. Therefore, the new standard becomes effective for the Company on January 1, 2018, with early application permitted for periods beginning on or after January 1, 2017. The standard permits the use of two transition methods on adoption, either retrospectively to each prior period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings of the annual reporting period that includes the date of initial application (modified retrospective method). Since the issuance of ASU 2014‑09, the FASB has issued several amendments which clarify certain points in the new Topic 606 - Revenue from Contracts with Customers, including ASU 2016‑08 (“Principal versus Agent Considerations—Reporting Revenue Gross versus Net”), ASU 2016‑10 (“Identifying Performance Obligations and Licensing”), ASU 2016‑11 (“Rescission of SEC Guidance Because of Accounting Standards Updates 2014‑09 and 2014‑16 Pursuant to Staff Announcements at the March 3, 2016 EITF Meeting”) and ASU 2016‑12 (“Narrow-Scope Improvements and Practical Expedients”). The Company plans to adopt all these standards using the modified retrospective method on January 1, 2018, and will modify its accounting policies to reflect the requirements of these standards. The Company expects to record an increase in current assets of $5.0 million related to the first milestone under the Company’s license with Kyowa Hakko Kirin Co., Ltd. (“KHK”), which the Company believes is not materially at risk, an increase in current liabilities of $1.0 million related to the corresponding payment to AstraZeneca AB (“AstraZeneca”), in accordance with the Company’s termination agreement and a related decrease in its accumulated deficit of approximately $4.0 million when it adopts the new standards on January 1, 2018, as Topic 606 permits revenue from certain milestones to be recognized earlier than Topic 605, the U.S. GAAP that is being superseded.

In February 2016, the FASB issued ASU No. 2016‑02, Leases (Topic 842), which replaces most current lease guidance when it becomes effective. This standard update intends to increase the transparency and improve comparability by requiring entities to recognize assets and liabilities on the balance sheet for all leases, with certain exceptions. The new standard states that a lessee will recognize a lease liability for the obligation to make lease payments and a right-of-use asset for the right to use the underlying asset for the lease term. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the consolidated statements of operations. The new guidance will be effective for the Company starting in the first quarter of fiscal 2019. Early adoption is permitted. The Company plans to adopt the new guidance effective January 1, 2019, and is currently evaluating the effect that this guidance will have on its consolidated financial statements and related disclosures.

In October 2016, the FASB issued ASU No. 2016‑16, Income Taxes: Intra-Entity Transfers of Assets Other Than Inventory (ASU 2016‑16). This update is to improve the accounting for the income tax consequences of intra-entity transfers of assets other than inventory. ASU 2016‑16 amends the guidance to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. Consequently, the amendments in this update eliminate the exception for an intra-entity transfer of an asset other than inventory. The amendments in this update do not include new disclosure requirements; however, existing disclosure requirements might be applicable when accounting for the current and deferred income taxes for an intra-entity transfer of an asset other than inventory. ASU 2016‑16 is effective for the Company’s interim and annual reporting periods during the year ending December 31, 2018, and all annual and interim reporting periods thereafter. Early adoption is permitted. The adoption of ASU 2016‑16 is not expected to have a material effect on the Company’s consolidated financial statements.

In May 2017, FASB issued ASU No. 2017‑09, Compensation-Stock Compensation (Topic 718) - Scope of Modification Accounting (ASU 2017‑09). The amendments included in this update provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The amendments in this update will be applied prospectively to an award modified on or after the adoption date. The amendments in ASU 2017‑09 are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.

The Company has reviewed all other significant newly-issued accounting pronouncements and concluded that they either are not applicable to the Company’s operations or that no material effect is expected on its consolidated financial statements as a result of future adoption.

Cash, Cash Equivalents and Investments

12 Months Ended

Dec. 31, 2017

Cash and Cash Equivalents [Abstract]

Cash, Cash Equivalents and Investments

3. CASH, CASH EQUIVALENTS AND INVESTMENTS

Securities classified as cash, cash equivalents and short-term investments as of December 31, 2017 and December 31, 2016 are summarized below (in thousands). Estimated fair value is based on quoted market prices for these investments.


	December 31, 2017
	Amortized		Gross Unrealized
	Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	5,882	$	—	$	—	$	5,882
Money market funds		68,651		—		—		68,651
Commercial paper		850		—		—		850
Total cash and cash equivalents		75,383		—		—		75,383
Short-term investments
U.S. treasury securities		3,994		—		(1)		3,993
Corporate bonds		26,853		—		(26)		26,827
Commercial paper		19,584		—		(14)		19,570
Asset-backed securities		8,209		—		(6)		8,203
Total short-term investments		58,640		—		(47)		58,593
Total cash equivalents and investments	$	134,023	$	—	$	(47)	$	133,976


	December 31, 2016
	Amortized		Gross Unrealized
	Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,638	$	—	$	—	$	3,638
Money market funds		68,561		—		—		68,561
Commercial paper		2,399		—		—		2,399
Total cash and cash equivalents		74,598		—		—		74,598
Short-term investments
Corporate bonds		58,464		2		(56)		58,410
Commercial paper		62,946		5		(20)		62,931
Asset-backed securities		4,886		—		(2)		4,884
Total short-term investments		126,296		7		(78)		126,225
Total cash equivalents and investments	$	200,894	$	7	$	(78)	$	200,823

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 consolidated 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 to date have been insignificant and are included in “other income, net” in the consolidated statements of operations.

All available-for-sale securities held as of December 31, 2017 and 2016, 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, 2017 and 2016, no investment was in a continuous unrealized loss position for more than one year, the unrealized losses were not due to a change in credit risk, and the Company believes that is more likely than not the investments will be held until maturity or a forecasted recovery of fair value.

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

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. 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 the quoted prices in active markets 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 measured on a recurring basis by level within the fair value hierarchy:


	December 31, 2017
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	68,651	$	68,651	$	—	$	—
U.S. treasury securities		3,993		3,993		—		—
Corporate bonds		26,827		—		26,827		—
Commercial paper		20,420		—		20,420		—
Asset-backed securities		8,203		—		8,203		—
Total	$	128,094	$	72,644	$	55,450	$	—


	December 31, 2016
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	68,561	$	68,561	$	—	$	—
Corporate bonds		58,410		—		58,410		—
Commercial paper		65,330		—		65,330		—
Asset-backed securities		4,884		—		4,884		—
Total	$	197,185	$	68,561	$	128,624	$	—

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. government-sponsored agency bonds as Level 1. When quoted market prices are not available for the specific security, then the Company estimates fair value by using benchmark yields, reported trades, broker/dealer quotes and issuer spreads. The Company classifies corporate bonds, commercial paper and asset-backed securities 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.

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, 2017 and December 31, 2016, 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

Property and Equipment

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property and Equipment

5. PROPERTY AND EQUIPMENT

Property and equipment consist of the following:


	December 31,
	2017		2016
	(in thousands)
Laboratory equipment	$	6,857	$	5,487
Office equipment and furniture		815		824
Leasehold improvements		7,949		7,783
Property and equipment, gross		15,621		14,094
Less: accumulated depreciation		(7,589)		(5,103)
Total property and equipment, net	$	8,032	$	8,991

Depreciation expense totaled $2.6 million, $1.3 million and $0.8 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Accrued and Other Liabilities

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

Accrued and Other Liabilities

6. ACCRUED AND OTHER LIABILITIES

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


	December 31,
	2017		2016
Accrued clinical and non-clinical expenses	$	5,447	$	6,694
Accrued contract manufacturing		3,980		2,705
Accrued professional and consulting services		530		322
Other		752		684
	$	10,709	$	10,405

Collaboration and Licensing Agreements	12 Months Ended
Collaboration and Licensing Agreements	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration and Licensing Agreements	7. COLLABORATION AND LICENSING AGREEMENTS KHK In November 2017, the Company entered into an exclusive license agreement with KHK (the “KHK Agreement”) for the development, commercialization and distribution of tenapanor in Japan. Under the terms of the KHK Agreement, the Company received an aggregate of $30.0 million in up-front license fees which was recognized as revenue when the agreement was executed. In addition, the Company may be entitled to receive up to $130 million in additional development and commercialization milestones based upon currency exchange rates as of the effective date of license agreement, 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. Shanghai Fosun Pharmaceutical Industrial Development Co. Ltd. (“Fosun Pharma”) In December 2017, the Company entered into an exclusive license agreement with Fosun Pharma (the “Fosun Agreement”) for the development, commercialization and distribution of tenapanor in China. Under the terms of the Fosun Agreement, the Company will receive an aggregate of $12.0 million in up-front license fees which was recognized as revenue when the agreement was executed. In addition, the Company may be entitled to additional milestones of up to $113 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%. AstraZeneca In October 2012, the Company entered into a collaboration partnership with AstraZeneca for the worldwide development and commercialization of tenapanor. Under the terms of the AstraZeneca collaboration partnership agreement, or the AstraZeneca Agreement, the Company received an aggregate of $75 million in up-front license and milestone fees. The amounts were recorded as deferred revenue when received and were recognized as revenue on a straight-line basis over the remaining estimated period of performance under the AstraZeneca Agreement. In June 2015, the Company entered into a termination agreement with AstraZeneca (the “Termination Agreement”) pursuant to which all licenses granted to AstraZeneca to the Company’s portfolio of NHE3 inhibitors, including the Company’s lead product candidate, tenapanor, were terminated, except for the limited purpose of allowing AstraZeneca to satisfy its obligations under the Termination Agreement. As the AstraZeneca Agreement was terminated in June 2015, the Company recognized the remaining deferred revenue balance of $43.1 million during the three months ended June 30, 2015. In the three months ended June 30, 2015, the Company recorded a $15.0 million payment for the return of the licenses as well as a $10.0 million payment for reimbursement of research and development expenses and the acceleration of the transfer of information and materials as a reduction in licensing revenue in the consolidated statements of operations. There has been no recognition of licensing revenue or collaborative development revenue since the termination of the AstraZeneca Agreement in 2015. 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 us or our licensees, and (ii) 20% of non-royalty revenue received from a new collaboration partner should we elect to license, or otherwise provide rights to develop and commercialize tenapanor or another NHE3 inhibitor, up to a maximum of $75.0 million in aggregate for (i) and (ii). We recognized $8.4 million, being 20% of the combined license revenue recognized under the KHK Agreement and Fosun Agreement, as cost of revenue in the year ended December 31, 2017.

Equity Incentive Plans

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

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. Effective January 1, 2018, the 2014 Plan share reserve was increased by 1,901,399 shares.

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, 2017, 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 three years ended December 31, 2017:


		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, 2014	1,265,282	1,007,724	$	5.51
Options authorized	743,569	—	$	—
Options granted	(379,709)	379,709	$	19.60
Options exercised	—	(77,784)	$	1.42
Options canceled	28,563	(28,563)	$	12.41
Issuance of common stock for services and restricted stock units	(23,285)	—		—
Balance at December 31, 2015	1,634,420	1,281,086	$	9.78
Options authorized	1,038,595	—	$	—
Options granted	(1,524,014)	1,524,014	$	11.42
Options exercised	—	(25,134)	$	2.19
Options canceled	67,743	(67,743)	$	16.67
Issuance of common stock for services and restricted stock units, net of 5,000 forfeitures	(189,507)	—	$	—
Balance at December 31, 2016	1,027,237	2,712,223	$	10.60
Options authorized	1,892,376	—	$	—
Options granted	(1,723,906)	1,723,906	$	11.73
Options exercised	—	(35,759)	$	1.70
Options canceled	445,029	(445,029)	$	14.15
Issuance of common stock for services and restricted stock units, net of 79,850 forfeitures	(601,008)	—	$	—
Balance at December 31, 2017	1,039,728	3,955,341	$	10.78	7.67	$	4,393
Vested and expected to vest at December 31, 2017		3,840,963	$	10.74	7.63	$	4,363
Exercisable at December 31, 2017		1,978,711	$	9.74	6.55	$	3,767

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, 2017, based on the Company’s common stock closing price of $6.60 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, 2017, 2016 and 2015, was $0.3 million, $0.3 million and $1.1 million, respectively.

The weighted-average grant-date estimated fair value of options granted during the years ended December 31, 2017, 2016 and 2015 was $8.19, $7.69 and $12.91 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,
	2017		2016		2015
Expected term (years)	5.93		5.99		5.89
Expected volatility	82	%	77	%	75	%
Risk-free interest rate	2.08	%	1.62	%	1.64	%
Dividend yield	—	%	—	%	—	%

Expected Term—The Company has very 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. Prior to December 31, 2016, the expected stock price volatility was calculated based on the average historical volatility for comparable publicly traded pharmaceutical companies. The Company selected companies with comparable characteristics, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the Company’s stock-based awards.

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 three years ended December 31, 2017:


					Weighted-
		Weighted-Average		Number of	Average Grant
	Number of Service-	Grant Date Fair		Performance-	Date Fair Value
	Based RSUs	Value Per Share		Based RSUs	Per Share
Non-vested restricted stock units at December 31, 2014	—	$	—	—	$	—
Granted	10,000	$	18.04	—	$	—
Non-vested restricted stock units at December 31, 2015	10,000	$	18.04	—	$	—
Granted	174,389	$	14.34	—	$	—
Vested	(5,000)	$	18.04	—	$	—
Forfeited	(5,000)	$	18.04	—	$	—
Non-vested restricted stock units at December 31, 2016	174,389	$	14.34	—	$	—
Granted	472,135	$	4.70	161,865	$	13.90
Vested	(43,597)	$	14.34	—	$	—
Forfeited	(61,865)	$	13.36	(17,985)	$	13.90
Non-vested restricted stock units at December 31, 2017	541,062	$	6.04	143,880	$	13.90

RSUs 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 PRSU awards to senior management which vest upon the achievement of certain performance conditions, subject to each employee’s continued service relationship with the Company. None of the PRSUs vested during the year ended December 31, 2017. When achievement of the performance conditions is considered probable, 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 estimated vesting period. The Company recognized $1.0 million of related expense during the year ended December 31, 2017.

The total estimated fair value of RSUs vested during the years ended December 31, 2017, 2016 and 2015 was $0.4 million, $0.1 million and nil, respectively.

Issuance of Common Stock for Services

During the years ended December 31, 2017, 2016 and 2015, the Company issued 46,858, 20,118 and 13,285 shares of common stock under the 2014 Plan in exchange for services performed, respectively, valued at $0.2 million, $0.2 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 three years ended December 31, 2017:


	Shares Available	Number of Shares	Purchase Price
	for Grant	Purchased	per Share		Gross Proceeds
					(in thousands)
Balance at December 31, 2014	202,762	—
Shares authorized	185,892	—
Shares purchased	(41,580)	41,580	$	13.25	$	551
Balance at December 31, 2015	347,074	41,580
Shares purchased	(69,054)	69,054	$	8.34	$	576
Balance at December 31, 2016	278,020	110,634
Shares purchased	(99,343)	99,343	$	6.27	$	623
Balance at December 31, 2017	178,677	209,977

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,
	2017		2016		2015
Expected term (years)	0.5		0.5		0.5
Expected volatility	80	%	76	%	97	%
Risk-free interest rate	0.97	%	0.48	%	0.16	%
Dividend yield	—	%	—	%	—	%

Stock-based Compensation

Total stock-based compensation recognized was as follows (in thousands):


	Year Ended December 31,
	2017		2016		2015
	(in thousands)
Research and development	$	4,585	$	2,786	$	1,327
General and administrative		5,005		2,531		1,307
Total stock-based compensation	$	9,590	$	5,317	$	2,634

As of December 31, 2017, the Company had $14.5 million, $2.5 million, $0.9 million and $0.1 million of total unrecognized compensation expense, net of estimated forfeitures, related to stock options, RSUs, PRSUs and ESPP, respectively, that will be recognized over an average vesting period of 2.43 years, 1.55 years, 0.83 years and 0.16 years, respectively.

Warrants

12 Months Ended

Dec. 31, 2017

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 has 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 during each of the years ended December 31, 2015, 2016 and 2017.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

10. INCOME TAXES

The components of the provision for income taxes for the year ended December 31, 2017, 2016 and 2015, are as follows (in thousands):


	Year Ended December 31,
	2017		2016		2015
Current:
Federal	$	—	$	—	$	(7)
State		5		—		(22)
Foreign		1,204		—		—
Total current		1,209		—		(29)
Deferred:
Federal		(30)		—		—
State		—		—		—
Foreign		—		—		—
Total deferred		(30)		—		—
Provision for (benefit from) income taxes	$	1,179	$	—	$	(29)

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


	December 31,
	2017		2016		2015
Income tax at the federal statutory rate	35.0	%	35.0	%	35.0	%
State taxes, net of federal benefit	0.5		0.3		(3.8)
Net impact related to foreign subsidiary	(1.2)		—		—
Change in valuation allowance	19.9		(36.2)		(30.7)
Impact of tax reform rate change	(56.4)		—		—
Tax credits	1.0		0.3		1.3
Other	(0.7)		0.6		(1.7)
Income tax provision	(1.9)	%	—	%	0.1	%

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, 2017 and 2016 (in thousands):


	December 31,
	2017		2016
	(in thousands)
Deferred tax assets:
Fixed assets and intangibles	$	30,804	$	—
Net operating loss carryforwards		22,355		68,639
Research credits		5,209		2,643
Stock-based compensation		3,159		2,583
Other		754		1,558
Gross deferred tax assets		62,281		75,423
Valuation allowance		(61,911)		(74,520)
Deferred tax assets net of valuation allowance		370		903
Deferred tax liabilities		(370)		(903)
Net deferred tax assets	$	—	$	—

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 piece of objective negative evidence evaluated was the cumulative loss incurred over the three-year periods ended December 31, 2017, 2016 and December 31, 2015. Such objective evidence limits the ability to consider other subjective evidence, such as the Company’s projections for future growth. On the basis of this evaluation, as of December 31, 2017 and 2016, 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.

Realization of deferred tax assets is dependent on future taxable income, if any, the timing and the amount of which are uncertain. The valuation allowance decreased by approximately $12.6 million during the year ended December 31, 2017, and increased by approximately $40.7 million and $9.1 million during the years ended December 31, 2016 and 2015, respectively. The decrease in the valuation allowance in the year ended December 31, 2017 primarily relates to the re-measurement of the deferred tax assets and liabilities due to the U.S. government’s enactment of comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (“TCJA”) on December 22, 2017, as discussed below.

The TCJA makes broad and complex changes to the U.S. tax code, including, but not limited to, reducing the U.S. federal corporate tax rate from 35% to 21%, effective January 1, 2018. The Company is able to determine a reasonable estimate of certain effects of the TCJA and has therefore recognized the provisional tax impacts related to the revaluation of deferred tax assets and liabilities. As a result, the Company has recorded a decrease related to net deferred tax assets of $35.6 million, with an offsetting change in valuation allowance of $35.6 million for the year ended December 31, 2017. The Securities and Exchange Commission has provided accounting and reporting guidance that allows the Company to report provisional amounts within a measurement period of up to one year from the date of enactment due to the complexities inherent in adopting the TCJA. The ultimate impact may differ from provisional amounts, possibly materially, due to, among other things, additional analysis, changes in interpretations and assumptions the Company has made, additional regulatory guidance that may be issued, and actions the Company may take as a result of the TCJA.

At December 31, 2017, the Company had net operating loss carryforwards for federal income tax purposes of approximately $149.4 million that expire beginning in 2030 if not utilized, federal research and development tax credit carryforwards of approximately $4.4 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 in 2030 if not utilized, and state research and development tax credit carryforwards of approximately $4.6 million which can be carried forward indefinitely. The Company had other state net operating losses of approximately $1.9 million that begin to expire in 2025. 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 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. The Company has previously completed a study in order to assess whether any ownership changes had arisen through December 31, 2014. As a result of the study, it was determined that the Company experienced an ownership change, as defined in Section 382, during May 2008. As a result of the analysis, it was determined that approximately $1.0 million of net operating losses and $49,000 of credit carryovers generated through May 2008 would expire prior to being utilized. No other ownership changes were identified through December 31, 2014. The Company is currently updating its Section 382 analysis but this analysis was not completed by year end. Preliminarily, it appears that there may be an additional ownership change in January 2016 which would impose further annual limitations on the utilization of operating loss and credit carryforwards. 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,
	2017		2016		2015
	(in thousands)
Balance at beginning of year	$	3,892	$	3,298	$	2,815
Additions (subtractions) based on tax positions related to prior year		16,103		45		(58)
Additions based on tax positions related to current year		739		549		541
Balance at end of year	$	20,734	$	3,892	$	3,298

The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $8.6 million, $3.5 million and $2.9 million as of December 31, 2017, 2016 and 2015, respectively.

The Company has elected to include interest and penalties as a component of tax expense. During the years ended December 31, 2017, 2016 and 2015, 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 change significantly during the next 12 months.

The Company files income tax returns in the U.S. federal, California, Maryland, Massachusetts, New Hampshire, New Jersey and Oregon tax jurisdictions. Due to the Company’s net operating loss and tax credit carryforwards, 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

12 Months Ended

Dec. 31, 2017

GEOGRAPHIC INFORMATION AND CONCENTRATIONS

GEOGRAPHIC INFORMATION AND CONCENTRATIONS

11. GEOGRAPHIC INFORMATION AND CONCENTRATIONS

Revenue by geographic areas for the years ended December 31, 2017, 2016 and 2015, are as follows (in thousands):


	Year Ended December 31,
	2017		2016		2015
United States	$	—	$	—	$	—
International:
Asia Pacific (1)		42,000		—		—
Europe (2)		—		—		24,026
Total revenue	$	42,000	$	—	$	24,026

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

(2)Revenues from Europe in 2015 comprised $24.0 million from Sweden in accordance with the AstraZeneca 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, 2017, 2016 and 2015, were wholly from collaboration partnerships. Collaboration partnerships accounting for more than 10% of total revenues during the years ended December 31, 2017, 2016 and 2015, are as follows:


	Year Ended December 31,
	2017		2016	2015
KHK	71	%	—	—
Fosun Pharma	29	%	—	—
AstraZeneca	—		—	100	%

Net Loss Per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Loss Per Share

12. 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, 2017, 2016 and 2015, 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,
	2017		2016		2015
Numerator:
Net loss	$	(64,339)	$	(112,387)	$	(29,621)
Denominator:
Weighted average number of shares outstanding—basic and diluted		47,435,331		40,118,522		22,892,640
Net loss per share - basic and diluted	$	(1.36)	$	(2.80)	$	(1.29)

For the years ended December 31, 2017, 2016 and 2015, 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,
	2017	2016	2015
Options to purchase common stock	3,977,160	2,464,089	1,241,741
Warrants to purchase common stock	2,172,899	2,172,899	1,268,021
Restricted stock units	323,819	87,079	603
Performance-based restricted stock units	148,216	—	—
ESPP shares issuable	60,524	37,227	21,077
Total	6,682,618	4,761,294	2,531,442

The number of potential common shares that would have been included in diluted income per share were it not 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, 2017, 2016 and 2015, was approximately 1.0 million, 0.8 million and 1.0 million, respectively.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

13. COMMITMENTS AND CONTINGENCIES

Leases

The Company has a lease agreement for a facility in Fremont, California 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 in Fremont, California to add space and to extend the lease term through September 2019. In addition, the amended lease agreement provides for a tenant improvement allowance of up to $0.6 million. 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 Third Amendment provides for a tenant improvement allowance of up to $0.4 million and the extended lease has rent escalation clauses throughout the lease term. It also provides a lease extension option for five years on 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.

Rent increases, including the impact of a rent holiday and leasehold improvement allowance from the landlord, will be recognized as deferred rent and amortized on a straight-line basis over the term of the lease. Under the terms of the lease agreement, the Company provided the lessor with a security deposit in the amount of $0.1 million. The lessor shall be entitled to draw on the security deposit in the event of any uncured default by the Company under the terms of the lease.

The future minimum payments under noncancelable operating leases at December 31, 2017, are as follows (in thousands):


Year Ended December 31,	Amounts
2018	$	1,615
2019		1,713
2020		2,026
2021		1,440
Thereafter		—
Total	$	6,794

Rent expense under operating leases was $1.7 million, $1.3 million and $0.9 million for the years ended December 31, 2017, 2016 and 2015, respectively.

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. This insurance 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, the Company believes that the amount, or range, of reasonably possible losses in connection with any pending actions against it in excess of established reserves, in the aggregate, not to be material to its consolidated financial condition or cash flows. However, losses may be material to the Company’s operating results for any particular future period, depending on the level of income or loss for such period.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

14. SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)

Selected quarterly financial results from operations for the years ended December 31, 2017 and 2016 are as follows (in thousands, except per share amounts):


	2017 Quarter End
	March 31		June 30		September 30		December 31
Total revenue	$	—	$	—	$	—	$	42,000
Gross profit		—		—		—		33,600
Operating expenses		28,434		26,418		21,225		22,638
Net income (loss)		(28,008)		(25,721)		(20,724)		10,114
Net income (loss) per share - basic	$	(0.59)	$	(0.54)	$	(0.44)	$	0.21
Net income (loss) per share - diluted	$	(0.59)	$	(0.54)	$	(0.44)	$	0.21


	2016 Quarter End
	March 31		June 30		September 30		December 31
Total revenue	$	—	$	—	$	—	$	—
Operating expenses		23,529		28,690		29,200		31,476
Net loss		(23,467)		(28,613)		(29,031)		(31,276)
Net loss per share - basic and diluted	$	(0.70)	$	(0.83)	$	(0.65)	$	(0.66)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Presentation

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

Principles of Consolidation

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

Property and Equipment

Impairment of Long-Lived Assets

Income Taxes

Revenue Recognition

Revenue subject to governmental withholding taxes is recognized on a gross basis with the withholding taxes recorded as a component of income tax expense.

Research and Development Costs

Accrued Research and Development Expenses

contract research organizations (“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

Comprehensive Loss

Net Loss per Share

Recent Accounting Pronouncements

Cash, Cash Equivalents and Investments (Tables)

12 Months Ended

Dec. 31, 2017

Cash and Cash Equivalents [Abstract]

Schedule of Securities Classified as Cash and Cash Equivalents and Short-term Investments


	December 31, 2017
	Amortized		Gross Unrealized
	Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	5,882	$	—	$	—	$	5,882
Money market funds		68,651		—		—		68,651
Commercial paper		850		—		—		850
Total cash and cash equivalents		75,383		—		—		75,383
Short-term investments
U.S. treasury securities		3,994		—		(1)		3,993
Corporate bonds		26,853		—		(26)		26,827
Commercial paper		19,584		—		(14)		19,570
Asset-backed securities		8,209		—		(6)		8,203
Total short-term investments		58,640		—		(47)		58,593
Total cash equivalents and investments	$	134,023	$	—	$	(47)	$	133,976


	December 31, 2016
	Amortized		Gross Unrealized
	Cost		Gains		Losses		Fair Value
Cash and cash equivalents:
Cash	$	3,638	$	—	$	—	$	3,638
Money market funds		68,561		—		—		68,561
Commercial paper		2,399		—		—		2,399
Total cash and cash equivalents		74,598		—		—		74,598
Short-term investments
Corporate bonds		58,464		2		(56)		58,410
Commercial paper		62,946		5		(20)		62,931
Asset-backed securities		4,886		—		(2)		4,884
Total short-term investments		126,296		7		(78)		126,225
Total cash equivalents and investments	$	200,894	$	7	$	(78)	$	200,823

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Summary of Fair Value Measurements of Company's Financial Assets


	December 31, 2017
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	68,651	$	68,651	$	—	$	—
U.S. treasury securities		3,993		3,993		—		—
Corporate bonds		26,827		—		26,827		—
Commercial paper		20,420		—		20,420		—
Asset-backed securities		8,203		—		8,203		—
Total	$	128,094	$	72,644	$	55,450	$	—


	December 31, 2016
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	68,561	$	68,561	$	—	$	—
Corporate bonds		58,410		—		58,410		—
Commercial paper		65,330		—		65,330		—
Asset-backed securities		4,884		—		4,884		—
Total	$	197,185	$	68,561	$	128,624	$	—

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment


	December 31,
	2017		2016
	(in thousands)
Laboratory equipment	$	6,857	$	5,487
Office equipment and furniture		815		824
Leasehold improvements		7,949		7,783
Property and equipment, gross		15,621		14,094
Less: accumulated depreciation		(7,589)		(5,103)
Total property and equipment, net	$	8,032	$	8,991

Accrued and Other Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

Schedule of Accrued Liabilities and Other Liabilities

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


	December 31,
	2017		2016
Accrued clinical and non-clinical expenses	$	5,447	$	6,694
Accrued contract manufacturing		3,980		2,705
Accrued professional and consulting services		530		322
Other		752		684
	$	10,709	$	10,405

Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2017

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

The following table summarizes activity under the 2008 Plan and the 2014 Plan, including grants issued to nonemployees, in the three years ended December 31, 2017:


		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, 2014	1,265,282	1,007,724	$	5.51
Options authorized	743,569	—	$	—
Options granted	(379,709)	379,709	$	19.60
Options exercised	—	(77,784)	$	1.42
Options canceled	28,563	(28,563)	$	12.41
Issuance of common stock for services and restricted stock units	(23,285)	—		—
Balance at December 31, 2015	1,634,420	1,281,086	$	9.78
Options authorized	1,038,595	—	$	—
Options granted	(1,524,014)	1,524,014	$	11.42
Options exercised	—	(25,134)	$	2.19
Options canceled	67,743	(67,743)	$	16.67
Issuance of common stock for services and restricted stock units, net of 5,000 forfeitures	(189,507)	—	$	—
Balance at December 31, 2016	1,027,237	2,712,223	$	10.60
Options authorized	1,892,376	—	$	—
Options granted	(1,723,906)	1,723,906	$	11.73
Options exercised	—	(35,759)	$	1.70
Options canceled	445,029	(445,029)	$	14.15
Issuance of common stock for services and restricted stock units, net of 79,850 forfeitures	(601,008)	—	$	—
Balance at December 31, 2017	1,039,728	3,955,341	$	10.78	7.67	$	4,393
Vested and expected to vest at December 31, 2017		3,840,963	$	10.74	7.63	$	4,363
Exercisable at December 31, 2017		1,978,711	$	9.74	6.55	$	3,767

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


	Year Ended December 31,
	2017		2016		2015
Expected term (years)	5.93		5.99		5.89
Expected volatility	82	%	77	%	75	%
Risk-free interest rate	2.08	%	1.62	%	1.64	%
Dividend yield	—	%	—	%	—	%

Summary of Non-vested RSU Activity


					Weighted-
		Weighted-Average		Number of	Average Grant
	Number of Service-	Grant Date Fair		Performance-	Date Fair Value
	Based RSUs	Value Per Share		Based RSUs	Per Share
Non-vested restricted stock units at December 31, 2014	—	$	—	—	$	—
Granted	10,000	$	18.04	—	$	—
Non-vested restricted stock units at December 31, 2015	10,000	$	18.04	—	$	—
Granted	174,389	$	14.34	—	$	—
Vested	(5,000)	$	18.04	—	$	—
Forfeited	(5,000)	$	18.04	—	$	—
Non-vested restricted stock units at December 31, 2016	174,389	$	14.34	—	$	—
Granted	472,135	$	4.70	161,865	$	13.90
Vested	(43,597)	$	14.34	—	$	—
Forfeited	(61,865)	$	13.36	(17,985)	$	13.90
Non-vested restricted stock units at December 31, 2017	541,062	$	6.04	143,880	$	13.90

Summary of Stock-Based Compensation Recognized

Total stock-based compensation recognized was as follows (in thousands):


	Year Ended December 31,
	2017		2016		2015
	(in thousands)
Research and development	$	4,585	$	2,786	$	1,327
General and administrative		5,005		2,531		1,307
Total stock-based compensation	$	9,590	$	5,317	$	2,634

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, 2014	202,762	—
Shares authorized	185,892	—
Shares purchased	(41,580)	41,580	$	13.25	$	551
Balance at December 31, 2015	347,074	41,580
Shares purchased	(69,054)	69,054	$	8.34	$	576
Balance at December 31, 2016	278,020	110,634
Shares purchased	(99,343)	99,343	$	6.27	$	623
Balance at December 31, 2017	178,677	209,977

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


	Year Ended December 31,
	2017		2016		2015
Expected term (years)	0.5		0.5		0.5
Expected volatility	80	%	76	%	97	%
Risk-free interest rate	0.97	%	0.48	%	0.16	%
Dividend yield	—	%	—	%	—	%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Summary of components of the provision for income taxes

The components of the provision for income taxes for the year ended December 31, 2017, 2016 and 2015, are as follows (in thousands):


	Year Ended December 31,
	2017		2016		2015
Current:
Federal	$	—	$	—	$	(7)
State		5		—		(22)
Foreign		1,204		—		—
Total current		1,209		—		(29)
Deferred:
Federal		(30)		—		—
State		—		—		—
Foreign		—		—		—
Total deferred		(30)		—		—
Provision for (benefit from) income taxes	$	1,179	$	—	$	(29)

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


	December 31,
	2017		2016		2015
Income tax at the federal statutory rate	35.0	%	35.0	%	35.0	%
State taxes, net of federal benefit	0.5		0.3		(3.8)
Net impact related to foreign subsidiary	(1.2)		—		—
Change in valuation allowance	19.9		(36.2)		(30.7)
Impact of tax reform rate change	(56.4)		—		—
Tax credits	1.0		0.3		1.3
Other	(0.7)		0.6		(1.7)
Income tax provision	(1.9)	%	—	%	0.1	%

Significant Components of the Company's Deferred Tax Assets


	December 31,
	2017		2016
	(in thousands)
Deferred tax assets:
Fixed assets and intangibles	$	30,804	$	—
Net operating loss carryforwards		22,355		68,639
Research credits		5,209		2,643
Stock-based compensation		3,159		2,583
Other		754		1,558
Gross deferred tax assets		62,281		75,423
Valuation allowance		(61,911)		(74,520)
Deferred tax assets net of valuation allowance		370		903
Deferred tax liabilities		(370)		(903)
Net deferred tax assets	$	—	$	—

Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits


	December 31,
	2017		2016		2015
	(in thousands)
Balance at beginning of year	$	3,892	$	3,298	$	2,815
Additions (subtractions) based on tax positions related to prior year		16,103		45		(58)
Additions based on tax positions related to current year		739		549		541
Balance at end of year	$	20,734	$	3,892	$	3,298

GEOGRAPHIC INFORMATION AND CONCENTRATIONS (Tables)

12 Months Ended

Dec. 31, 2017

GEOGRAPHIC INFORMATION AND CONCENTRATIONS

Summary of revenue by geographic areas

Revenue by geographic areas for the years ended December 31, 2017, 2016 and 2015, are as follows (in thousands):


	Year Ended December 31,
	2017		2016		2015
United States	$	—	$	—	$	—
International:
Asia Pacific (1)		42,000		—		—
Europe (2)		—		—		24,026
Total revenue	$	42,000	$	—	$	24,026

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

(2)Revenues from Europe in 2015 comprised $24.0 million from Sweden in accordance with the AstraZeneca Agreement.

Schedules of collaboration partnerships


	Year Ended December 31,
	2017		2016	2015
KHK	71	%	—	—
Fosun Pharma	29	%	—	—
AstraZeneca	—		—	100	%

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Computation of Net Loss Per Common Share

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,
	2017		2016		2015
Numerator:
Net loss	$	(64,339)	$	(112,387)	$	(29,621)
Denominator:
Weighted average number of shares outstanding—basic and diluted		47,435,331		40,118,522		22,892,640
Net loss per share - basic and diluted	$	(1.36)	$	(2.80)	$	(1.29)

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


	Year Ended December 31,
	2017	2016	2015
Options to purchase common stock	3,977,160	2,464,089	1,241,741
Warrants to purchase common stock	2,172,899	2,172,899	1,268,021
Restricted stock units	323,819	87,079	603
Performance-based restricted stock units	148,216	—	—
ESPP shares issuable	60,524	37,227	21,077
Total	6,682,618	4,761,294	2,531,442

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments Under the Noncancelable Operating Lease

The future minimum payments under noncancelable operating leases at December 31, 2017, are as follows (in thousands):


Year Ended December 31,	Amounts
2018	$	1,615
2019		1,713
2020		2,026
2021		1,440
Thereafter		—
Total	$	6,794

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of Selected Quarterly Financial Results from Operations

Selected quarterly financial results from operations for the years ended December 31, 2017 and 2016 are as follows (in thousands, except per share amounts):


	2017 Quarter End
	March 31		June 30		September 30		December 31
Total revenue	$	—	$	—	$	—	$	42,000
Gross profit		—		—		—		33,600
Operating expenses		28,434		26,418		21,225		22,638
Net income (loss)		(28,008)		(25,721)		(20,724)		10,114
Net income (loss) per share - basic	$	(0.59)	$	(0.54)	$	(0.44)	$	0.21
Net income (loss) per share - diluted	$	(0.59)	$	(0.54)	$	(0.44)	$	0.21


	2016 Quarter End
	March 31		June 30		September 30		December 31
Total revenue	$	—	$	—	$	—	$	—
Operating expenses		23,529		28,690		29,200		31,476
Net loss		(23,467)		(28,613)		(29,031)		(31,276)
Net loss per share - basic and diluted	$	(0.70)	$	(0.83)	$	(0.65)	$	(0.66)

Organization and Basis of Presentation - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	1

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended			24 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2014
Organization And Basis Of Presentation [Line Items]
Increase in current assets	$ 149,712,000				$ 203,992,000				$ 149,712,000	$ 203,992,000		$ 149,712,000
Increase in current liabilities	17,871,000				19,201,000				17,871,000	19,201,000		17,871,000
Decrease in accumulated deficit	(278,214,000)				(213,875,000)				(278,214,000)	(213,875,000)		(278,214,000)
Net loss	10,114,000	$ (20,724,000)	$ (25,721,000)	$ (28,008,000)	(31,276,000)	$ (29,031,000)	$ (28,613,000)	$ (23,467,000)	$ (64,339,000)	(112,387,000)	$ (29,621,000)
Cash and cash equivalents original maturity dates									P90D
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.
Impairment loss of long lived assets									$ 0
Income tax provision (benefit)									1,179,000		(29,000)
Unrecognized excess tax benefit	20,734,000				$ 3,892,000				$ 20,734,000	$ 3,892,000	$ 3,298,000	20,734,000	$ 2,815,000
Accounts Receivable
Provision for doubtful accounts												0
Minimum [Member]
Organization And Basis Of Presentation [Line Items]
Property and equipment, estimated useful lives									3 years
Maximum [Member]
Organization And Basis Of Presentation [Line Items]
Property and equipment, estimated useful lives									5 years
Adjustments \| Adoption of new accounting pronouncement
Organization And Basis Of Presentation [Line Items]
Increase in current assets	(5,000,000)								$ (5,000,000)			(5,000,000)
Increase in current liabilities	(1,000,000)								(1,000,000)			(1,000,000)
Decrease in accumulated deficit	$ (4,000,000)								$ (4,000,000)			$ (4,000,000)

Cash, Cash Equivalents and Investments - Schedule of Securities Classified as Cash and Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	$ 75,383	$ 74,598	$ 107,004	$ 107,286
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	75,383	74,598
Short-term investments, Amortized Cost	58,640	126,296
Short-term investments, Gross Unrealized Gains	0	7
Short-term investments, Gross Unrealized Losses	(47)	(78)
Short-term investments, Fair Value	58,593	126,225
Cash equivalents and short-term investments, Amortized Cost	134,023	200,894
Cash equivalents and short-term investments, Gross Unrealized Gains	0	7
Cash equivalents and short-term investments, Gross Unrealized Losses	(47)	(78)
Cash equivalents and short-term investments, Fair Value	133,976	200,823
Cash [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	5,882	3,638
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	5,882	3,638
Money Market Funds [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	68,651	68,561
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	68,651	68,561
Commercial Paper (Cash Equivalents) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Cash and cash equivalents, Amortized Cost	850	2,399
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	850	2,399
US Treasury Securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	3,994
Short-term investments, Gross Unrealized Gains	0
Short-term investments, Gross Unrealized Losses	(1)
Short-term investments, Fair Value	3,993
Corporate Bonds (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	26,853	58,464
Short-term investments, Gross Unrealized Gains	0	2
Short-term investments, Gross Unrealized Losses	(26)	(56)
Short-term investments, Fair Value	26,827	58,410
Commercial Paper (Investments) [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	19,584	62,946
Short-term investments, Gross Unrealized Gains	0	5
Short-term investments, Gross Unrealized Losses	(14)	(20)
Short-term investments, Fair Value	19,570	62,931
Asset-Backed Securities [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Short-term investments, Amortized Cost	8,209	4,886
Short-term investments, Gross Unrealized Gains	0	0
Short-term investments, Gross Unrealized Losses	(6)	(2)
Short-term investments, Fair Value	$ 8,203	$ 4,884

Cash, Cash Equivalents and Investments - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017
Maximum [Member]
Cash Cash Equivalents And Short Term Investments [Line Items]
Available for sale securities contractual maturity period	1 year

Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Assets at fair value	$ 128,094	$ 197,185
Level 1 [Member]
Assets:
Assets at fair value	72,644	68,561
Level 2 [Member]
Assets:
Assets at fair value	55,450	128,624
Money Market Funds [Member]
Assets:
Assets at fair value	68,651	68,561
Money Market Funds [Member] \| Level 1 [Member]
Assets:
Assets at fair value	68,651	68,561
US Treasury Securities [Member]
Assets:
Assets at fair value	3,993
US Treasury Securities [Member] \| Level 1 [Member]
Assets:
Assets at fair value	3,993
Corporate Bonds [Member]
Assets:
Assets at fair value	26,827	58,410
Corporate Bonds [Member] \| Level 2 [Member]
Assets:
Assets at fair value	26,827	58,410
Commercial Paper [Member]
Assets:
Assets at fair value	20,420	65,330
Commercial Paper [Member] \| Level 2 [Member]
Assets:
Assets at fair value	20,420	65,330
Asset-Backed Securities [Member]
Assets:
Assets at fair value	8,203	4,884
Asset-Backed Securities [Member] \| Level 2 [Member]
Assets:
Assets at fair value	$ 8,203	$ 4,884

Fair Value Measurements - Additional Information (Detail)	Dec. 31, 2017 USD ($)
Fair Value Disclosures [Abstract]
Transfer of assets from Level 1 to Level 2	$ 0
Transfer of assets from Level 2 to Level 1	$ 0

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 15,621	$ 14,094
Less: accumulated depreciation	(7,589)	(5,103)
Total property and equipment, net	8,032	8,991
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	6,857	5,487
Office Equipment And Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	815	824
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,949	$ 7,783

Property and Equipment - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 2.6	$ 1.3	$ 0.8

Accrued and Other Liabilities - Schedule of Accrued Liabilities and Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued clinical and non-clinical expenses	$ 5,447	$ 6,694
Accrued contract manufacturing	3,980	2,705
Accrued professional and consulting services	530	322
Other	752	684
Accrued liabilities and other liabilities	$ 10,709	$ 10,405

Collaboration and Licensing Agreements - Additional Information (Detail) - USD ($)				1 Months Ended	3 Months Ended	6 Months Ended
	Dec. 31, 2017	Nov. 30, 2017	Oct. 31, 2012	Nov. 30, 2017	Jun. 30, 2015	Jun. 30, 2016
Development and Commercialization
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Future development milestones				$ 130,000,000
Kyowa Hakko Kirin [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Upfront payment received		$ 30,000,000
Shanghai Fosun Pharmaceutical Industrial Development [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Upfront payment received	$ 12,000,000
Future development milestones	$ 113,000,000
Threshold percentage of net sales for tiered royalties	20.00%
AstraZeneca [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Upfront payment received			$ 75,000,000
Amount of upfront payment for return of licenses					$ 15,000,000
Amount of reimbursement paid for certain research and development expenses in consideration of acceleration of transfer of information and materials					10,000,000
Recognized deferred revenue					$ 43,100,000
Recognition of licensing and collaborative development revenue						$ 0

Equity Incentive Plans - Additional Information (Detail) - USD ($)			12 Months Ended
	Jan. 01, 2018	Jun. 18, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 30, 2016	Jun. 30, 2015	Dec. 31, 2014
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			1,723,906	1,524,014	379,709
Weighted-average grant-date estimated fair value of options granted			$ 8.19	$ 7.69	$ 12.91
Estimated fair value of common stock			$ 6.60
Estimated fair value of options exercised during period			$ 300,000	$ 300,000	$ 1,100,000
Estimated fair value of restricted stock vested during period			400,000	100,000	0
Stock-based compensation			$ 9,590,000	$ 5,317,000	$ 2,634,000
Shares available for future grant			1,039,728	1,027,237	1,634,420			1,265,282
Purchase price of common shares							$ 10.70
Warrants issued to purchase common stock							2,172,899
Exercise price for warrants			$ 13.91				$ 13.91
Issuance of common stock for services (Shares)			46,858	20,118	13,285
Issuance of common stock for services, amount			$ 201,000	$ 187,000	$ 194,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum shares to be issued up on exercise of incentive stock options	1,901,399
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense			$ 100,000
Unrecognized stock based compensation expense, weighted-average remaining recognition period			1 month 28 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]
Incease 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			178,677	278,020	347,074			202,762
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 stock based compensation expense			$ 14,500,000
Unrecognized stock based compensation expense, weighted-average remaining recognition period			2 years 5 months 5 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense			$ 2,500,000
Unrecognized stock based compensation expense, weighted-average remaining recognition period			1 year 6 months 18 days
Performance-Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated fair value of restricted stock vested during period			$ 0
Stock-based compensation			1,000,000
Unrecognized stock based compensation expense			$ 900,000
Unrecognized stock based compensation expense, weighted-average remaining recognition period			9 months 29 days

Equity Incentive Plans - Summary of Activity Under 2008 Plan, 2014 Plan and Inducement Plan Including Grants to Nonemployees Issued (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Shares Available for Grant, Beginning balance	1,027,237	1,634,420	1,265,282
Shares Available for Grant, Options authorized	1,892,376	1,038,595	743,569
Shares Available for Grant, Options granted	(1,723,906)	(1,524,014)	(379,709)
Shares Available for Grant, Options exercised	0	0	0
Shares Available for Grant, Options canceled	445,029	67,743	28,563
Issuance of common stock for services and restricted stock units, net of forfeitures	601,008	189,507	23,285
Shares Available for Grant, Issuance of common stock for services	(46,858)	(20,118)	(13,285)
Shares Available for Grant, Ending balance	1,039,728	1,027,237	1,634,420
Options Issued and Outstanding Number of Shares, Beginning balance	2,712,223	1,281,086	1,007,724
Options Issued and Outstanding Number of Shares, Options authorized	0	0	0
Options Issued and Outstanding Number of Shares, Options granted	1,723,906	1,524,014	379,709
Options Issued and Outstanding Number of Shares, Options exercised	(35,759)	(25,134)	(77,784)
Options Issued and Outstanding Number, Options cancelled	(445,029)	(67,743)	(28,563)
Options Issued and Outstanding Number of Shares, Issuance of common stock for services	0	0	0
Options Issued and Outstanding Number of Shares, Ending balance	3,955,341	2,712,223	1,281,086
Options Issued and Outstanding Average Exercise Price per Share, Beginning balance	$ 10.60	$ 9.78	$ 5.51
Options Issued and Outstanding Number of Shares, Expected to vest	3,840,963
Options Issued and Outstanding Number of Shares, Exercisable	1,978,711
Options Issued and Outstanding Average Exercise Price per Share, Options granted	$ 11.73	11.42	19.60
Options Issued and Outstanding Average Exercise Price per Share, Options exercised	1.70	2.19	1.42
Options Issued and Outstanding Average Exercise Price per Share, Options canceled	14.15	16.67	12.41
Options Issued and Outstanding Average Exercise Price per Share, Issuance of common stock for services	0	0	0
Options Issued and Outstanding Average Exercise Price per Share, Ending balance	10.78	$ 10.60	$ 9.78
Options Issued and Outstanding Average Exercise Price per Share, Expected to vest	10.74
Options Issued and Outstanding Average Exercise Price per Share, Exercisable	$ 9.74
Weighted Average Remaining Contractual Term, Ending Balance	7 years 8 months 1 day
Weighted Average Remaining Contractual Term, Vested and Expected to Vest	7 years 7 months 17 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 6 months 18 days
Aggregate Intrinsic Value, Ending balance	$ 4,393
Aggregate Intrinsic Value, Expected to Vest	4,363
Aggregate Intrinsic Value, Exercisable	$ 3,767
Share available for grant, forfeitures	79,850	5,000

Equity Incentive Plans - Summary of Non-vested RSU Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Service Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Beginning balance	174,389	10,000
Number of Shares, Granted	472,135	174,389	10,000
Number of Shares, Vested	(43,597)	(5,000)
Number of Shares, Forfeited	(61,865)	(5,000)
Number of Shares, Ending balance	541,062	174,389	10,000
Weighted-Average Grant Date Fair Value Per Share, Beginning balance	$ 14.34	$ 18.04
Weighted-Average Grant Date Fair Value Per Share, Granted	4.70	14.34	$ 18.04
Weighted-Average Grant Date Fair Value Per Share, Vested	14.34	18.04
Weighted-Average Grant Date Fair Value Per Share, Forfeited	13.36	18.04
Weighted-Average Grant Date Fair Value Per Share, Ending balance	$ 6.04	$ 14.34	$ 18.04
Performance-Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted	161,865
Number of Shares, Forfeited	(17,985)
Number of Shares, Ending balance	143,880
Weighted-Average Grant Date Fair Value Per Share, Granted	$ 13.90
Weighted-Average Grant Date Fair Value Per Share, Forfeited	13.90
Weighted-Average Grant Date Fair Value Per Share, Ending balance	$ 13.90

Equity Incentive Plans - Summary of Weighted Average Assumptions to Estimate Fair value of Stock Option Awards and Employee Stock Purchase Plan (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term ( years)	5 years 11 months 5 days	5 years 11 months 27 days	5 years 10 months 21 days
Volatility	82.00%	77.00%	75.00%
Risk-free interest rate	2.08%	1.62%	1.64%
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term ( years)	6 months	6 months	6 months
Volatility	80.00%	76.00%	97.00%
Risk-free interest rate	0.97%	0.48%	0.16%

Equity Incentive Plans - Employee Stock Purchase Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Beginning balance	1,027,237	1,634,420	1,265,282
Shares Available for Grant, Shares authorized	1,892,376	1,038,595	743,569
Shares Available for Grant, Ending balance	1,039,728	1,027,237	1,634,420
Options Issued and Outstanding Number of Shares, Beginning balance	2,712,223	1,281,086	1,007,724
Options Issued and Outstanding Number of Shares, Ending balance	3,955,341	2,712,223	1,281,086
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Beginning balance	278,020	347,074	202,762
Shares Available for Grant, Shares authorized			185,892
Shares Available of Grant, Shares purchased	(99,343)	(69,054)	(41,580)
Shares Available for Grant, Ending balance	178,677	278,020	347,074
Options Issued and Outstanding Number of Shares, Beginning balance	110,634	41,580
Number of Shares Purchased	99,343	69,054	41,580
Options Issued and Outstanding Number of Shares, Ending balance	209,977	110,634	41,580
Purchase Price per Share	$ 6.27	$ 8.34	$ 13.25
Gross Proceeds	$ 623	$ 576	$ 551

Equity Incentive Plans - Summary of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 9,590	$ 5,317	$ 2,634
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	4,585	2,786	1,327
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 5,005	$ 2,531	$ 1,307

Warrants (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2017
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 beneficail ownership percentage	9.99%
Warrants exercised		0

Income Taxes - (Detail) - USD ($) $ in Thousands	12 Months Ended
Income Taxes - (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2015
Current:
Federal		$ (7)
State	$ 5	(22)
Foreign	1,204
Total Current	1,209	(29)
Deferred:
Federal	(30)
Total deferred	(30)
Provision for (benefit from) income taxes	$ 1,179	$ (29)

Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Iincome tax the federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	0.50%	0.30%	(3.80%)
Net impact related to foreign subsidiary	(1.20%)
Change in valuation allowance	19.90%	(36.20%)	(30.70%)
Impact of tax reform rate change	(56.40%)
Tax credits	1.00%	0.30%	1.30%
Other	(0.70%)	0.60%	(1.70%)
Income tax provisionl	(1.90%)	0.00%	0.10%

Income Taxes - Significant Components of the Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets, Net [Abstract]
Fixed assets and intangibles	$ 30,804	$ 0
Net operating loss carryforwards	22,355	68,639
Research credits	5,209	2,643
Stock awards	3,159	2,583
Other	754	1,558
Gross deferred tax assets	62,281	75,423
Valuation allowance	(61,911)	(74,520)
Total deferred tax assets net of valuation allowance	370	903
Deferred tax liabilities	(370)	(903)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Increase (decrease) in deferred tax valuation allowance		$ (12,600,000)	$ 40,700,000	$ 9,100,000
Iincome tax the federal statutory rate		35.00%	35.00%	35.00%
Decrease related to net federal deferred tax assets		$ 35,600,000
Offsetting change in valuation allowance		35,600,000
Accrued interest and penalties related to unrecognized tax benefits		0	$ 0	$ 0
Tax losst carryforward lost					$ 1,000,000
Tax credit carryforward lost					$ 49,000
Forecast
Income Tax Disclosure [Line Items]
Iincome tax the federal statutory rate	21.00%
Federal Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 149,400,000
Operating loss carryforward expiration year		2030
Federal Tax Authority [Member] \| Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 4,400,000
Tax credit carryforward expiration year		2027
State Tax Authority [Member]
Income Tax Disclosure [Line Items]
Operating loss carryforward expiration year		2025
Other net operating losses		$ 1,900,000
State Tax Authority [Member] \| California
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 88,300,000
Operating loss carryforward expiration year		2030
State Tax Authority [Member] \| Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 4,600,000
State Tax Authority [Member] \| Minimum Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards			$ 100,000
Foreign Tax Authority [Member]
Income Tax Disclosure [Line Items]
Foreign tax credit carryforwards		$ 1,200,000
Operating loss carryforward expiration year		2027

Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 3,892	$ 3,298	$ 2,815
Additions (subtractions) based on tax positions related to prior year	16,103	45	(58)
Additions based on tax positions related to current year	739	549	541
Balance at end of year	20,734	3,892	3,298
Unrecognized tax benefits that would affect the effective tax rate if recognized	$ 8,600	$ 3,500	$ 2,900

GEOGRAPHIC INFORMATION AND CONCENTRATIONS (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 42,000	$ 42,000	$ 24,026
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue		42,000
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue			24,026
Japan
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue		30,000
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue		$ 12,000
Sweden
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue			$ 24,000

GEOGRAPHIC INFORMATION AND CONCENTRATIONS - Concentration Risk (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
KHK
Concentration Risk [Line Items]
Percentage of revenue	71.00%
Fosun Pharma
Concentration Risk [Line Items]
Percentage of revenue	29.00%
AstraZeneca
Concentration Risk [Line Items]
Percentage of revenue		100.00%

Net Loss Per Share - Computation of Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net loss	$ 10,114	$ (20,724)	$ (25,721)	$ (28,008)	$ (31,276)	$ (29,031)	$ (28,613)	$ (23,467)	$ (64,339)	$ (112,387)	$ (29,621)
Denominator:
Weighted average number of shares outstanding-basic and diluted									47,435,331	40,118,522	22,892,640
Net loss per share-basic and diluted					$ (0.66)	$ (0.65)	$ (0.83)	$ (0.70)	$ (1.36)	$ (2.80)	$ (1.29)

Net Loss per Share - Calculation of Anti-dilutive Potentially Dilutive Securities Not Included in Diluted Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	6,682,618	4,761,294	2,531,442
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	1,000,000	800,000	1,000,000
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	3,977,160	2,464,089	1,241,741
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	2,172,899	2,172,899	1,268,021
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	323,819	87,079	603
Performance-Based Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	148,216
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	60,524	37,227	21,077

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	May 31, 2016	Sep. 30, 2014	Dec. 31, 2012	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Security deposit provided to lessor				$ 100,000
Rent expense under operating leases				$ 1,700,000	$ 1,300,000	$ 900,000
December 2012, Amended Facility Lease Agreement [Member]
Loss Contingencies [Line Items]
Lease expiration date			Sep. 30, 2016
September 2014, Amended Facility Lease Agreement [Member]
Loss Contingencies [Line Items]
Lease expiration date		Sep. 30, 2019
Lease improvement allowance maximum amount		$ 600,000
May 2016, Amended Facility Lease Agreement [Member]
Loss Contingencies [Line Items]
Lease expiration date	Sep. 30, 2021
Lease improvement allowance maximum amount	$ 400,000

Commitments and Contingencies - Schedule of Future Minimum Payments Under the Noncancelable Operating Lease (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2018	$ 1,615
2019	1,713
2020	2,026
2021	1,440
Total	$ 6,794

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Results from Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 42,000								$ 42,000		$ 24,026
Gross profit	33,600								33,600		24,026
Operating expenses	22,638	$ 21,225	$ 26,418	$ 28,434	$ 31,476	$ 29,200	$ 28,690	$ 23,529	98,715	$ 112,895	53,415
Net (loss) income	$ 10,114	$ (20,724)	$ (25,721)	$ (28,008)	$ (31,276)	$ (29,031)	$ (28,613)	$ (23,467)	$ (64,339)	$ (112,387)	$ (29,621)
Net (loss) income per share:
Net loss per share - basic and diluted					$ (0.66)	$ (0.65)	$ (0.83)	$ (0.70)	$ (1.36)	$ (2.80)	$ (1.29)
Net income (loss) per share - basic	$ 0.21	$ (0.44)	$ (0.54)	$ (0.59)
Net income (loss) per share - diluted	$ 0.21	$ (0.44)	$ (0.54)	$ (0.59)