Accounting Policies [Abstract] Accounting Policies [Abstract] Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block] Accrued and Other Liabilities Accounts Payable, Current Accounts payable Accretion (Amortization) of Discounts and Premiums, Investments Amortization of premium on investment securities Accrued clinical trial expenses. Accrued Clinical Trial Expenses Accrued clinical trial expenses Accrued contract manufacturing costs. Accrued Contract Manufacturing Costs Accrued contract manufacturing Accrued Liabilities and Other Liabilities Accrued and other liabilities Accrued liabilities and other liabilities Accrued professional and consultant fees current. Accrued Professional And Consultant Fees Current Accrued professional and consulting services Accrued research and development expenses policy. Accrued Research and Development Expenses Policy [Policy Text Block] Accrued Research and Development Expenses Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive loss Additional Paid in Capital, Common Stock Additional paid-in capital Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net loss to net cash used in operating activities: Allocated Share-based Compensation Expense Stock-based compensation Amendment Flag Amendment Flag Amortization of Debt Issuance Costs Amortization of deferred financing costs Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Anti-dilutive securities excluded from computation of diluted net loss per share attributable to common stockholders Asset-backed Securities [Member] Asset-Backed Securities [Member] Assets Total assets Assets [Abstract] Assets Assets, Current Total current assets Assets, Current [Abstract] Current assets: Assets, Fair Value Disclosure Assets at fair value Assets, Fair Value Disclosure [Abstract] Assets: Available-for-sale Securities Short-term investments, Fair Value Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Short-term investments, Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Short-term investments, Gross Unrealized Losses Available-for-sale Securities, Amortized Cost Basis Short-term investments, Amortized Cost Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Investment in continuous unrealized loss position for more than one year Available for sale securities contractual maturity period. Available For Sale Securities Contractual Maturity Period Available for sale securities contractual maturity period Available-for-sale Securities, Debt Securities, Current Short-term investments Award Type [Axis] Award Type [Axis] Cash and Cash Equivalents [Abstract] Cash and Cash Equivalents [Abstract] Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Cash and cash equivalents at beginning of period Cash and cash equivalents Cash and cash equivalents, Amortized Cost Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents, Fair Value Disclosure Cash and cash equivalents, Fair Value Cash and cash equivalents gross unrealized gains. Cash And Cash Equivalents Gross Unrealized Gains Cash and cash equivalents, Gross Unrealized Gains Cash and cash equivalents gross unrealized losses. Cash And Cash Equivalents Gross Unrealized Losses Cash and cash equivalents, Gross Unrealized Losses Cash and Cash Equivalents, Period Increase (Decrease) Net (decrease) increase in cash and cash equivalents Cash, Cash Equivalents, and Short-term Investments Cash equivalents and short-term investments, Amortized Cost Cash, cash equivalents and short term investments fair value disclosure. Cash Cash Equivalents And Short Term Investments Fair Value Disclosure Cash equivalents and short-term investments, Fair Value Cash, cash equivalents and short term investments gross unrealized gains. Cash Cash Equivalents And Short Term Investments Gross Unrealized Gains Cash equivalents and short-term investments, Gross Unrealized Gains Cash, cash equivalents and short term investments gross unrealized losses. Cash Cash Equivalents And Short Term Investments Gross Unrealized Losses Cash equivalents and short-term investments, Gross Unrealized Losses Cash and cash equivalents and short term investments. Cash Cash Equivalents And Short Term Investments [Line Items] Cash Cash Equivalents And Short Term Investments [Line Items] Cash and cash equivalents and short term investments. Cash Cash Equivalents And Short Term Investments [Table] Cash Cash Equivalents And Short Term Investments [Table] Cash, Cash Equivalents, and Short-term Investments [Text Block] Cash, Cash Equivalents and Investments Cash [Member] Cash [Member] Class of Warrant or Right, Exercise Price of Warrants or Rights Purchase price for warrants Class of warrant or right expiration date description. Class Of Warrant Or Right Expiration Date Description Warrants description Class of Warrant or Right, Number of Securities Called by Warrants or Rights Warrants issued to purchase common stock Class of warrant or right number of warrants exercised. Class Of Warrant Or Right Number Of Warrants Exercised Number of warrants exercised Commercial Paper Cash Equivalents Including Securities [Member] Commercial Paper Cash Equivalents Including Securities [Member] Commercial Paper [Member] Commercial Paper [Member] Commercial Paper (Cash Equivalents) [Member] Commercial Paper, Not Included with Cash and Cash Equivalents [Member] Commercial Paper (Investments) [Member] Commitments and Contingencies Commitments and contingencies Common Stock, Par or Stated Value Per Share Common stock, par value Common Stock, Shares Authorized Common stock, shares authorized Common Stock, Shares, Issued Common stock, shares issued Common Stock, Shares, Outstanding Common stock, shares outstanding Common Stock, Value, Issued Common stock, $0.0001 par value; 300,000,000 shares authorized as of March 31, 2017 and December 31, 2016, respectively; 47,386,756 and 47,309,422 shares issued and outstanding as of March 31, 2017 and December 31, 2016, respectively. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive loss Corporate Debt Securities [Member] Corporate Bonds (Investments) [Member] Cost of Services, Amortization Amortization of deferred compensation for services Current Fiscal Year End Date Current Fiscal Year End Date Depreciation Depreciation expense Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Stock-Based Compensation Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Document Fiscal Year Focus Document Fiscal Year Focus Document Period End Date Document Period End Date Document Type Document Type Domestic Corporate Debt Securities Including Cash Equivalents [Member] Domestic Corporate Debt Securities Including Cash Equivalents [Member] Corporate Bonds [Member] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Earnings Per Share, Basic and Diluted Net loss per common share, basic and diluted Net loss per share - basic and diluted Earnings Per Share [Text Block] Net Loss Per Share Employee-related Liabilities, Current Accrued compensation and benefits Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Unrecognized stock based compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Unrecognized stock based compensation expense, weighted-average remaining recognition period Employee Stock Option [Member] Options to Purchase Common Stock [Member] Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] Entity Central Index Key Entity Central Index Key Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Filer Category Entity Filer Category Entity Registrant Name Entity Registrant Name Equity [Abstract] Equity [Abstract] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Assets, Level 1 to Level 2 Transfers, Amount Transfer of assets from Level 1 to Level 2 Fair Value, Assets, Level 2 to Level 1 Transfers, Amount Transfer of assets from Level 2 to Level 1 Fair Value, Assets Measured on Recurring Basis [Table Text Block] Summary of Fair Value Measurements of Company's Financial Assets Asset Class [Domain] Asset Class [Domain] Asset Class [Axis] Asset Class [Axis] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Fair Value Disclosures [Text Block] Fair Value Measurements Fair Value, Inputs, Level 1 [Member] Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Level 2 [Member] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value Measurement, Policy [Policy Text Block] Fair Value Measurements Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Measurements, Recurring [Member] Fair Value, Recurring [Member] General and Administrative Expense General and administrative General and Administrative Expense [Member] General and Administrative [Member] Gross Proceeds From Issuance Of Common Stock Gross Proceeds From Issuance Of Common Stock Gross proceeds from issuance of common stock Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Loss before provision for income taxes Income Statement [Abstract] Income Statement [Abstract] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Income Tax Expense (Benefit) Provision for income taxes Increase (Decrease) in Accounts Payable Accounts payable Increase (Decrease) in Employee Related Liabilities Accrued compensation and benefits Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Increase (Decrease) in Other Accrued Liabilities Accrued and other liabilities Increase (Decrease) in Prepaid Expense and Other Assets Prepaid expenses and other assets Investment Warrants, Exercise Price Warrants exercise price per share Liabilities Total liabilities Liabilities and Equity Total liabilities and stockholders' equity Liabilities and Equity [Abstract] Liabilities and stockholders' equity Liabilities, Current Total current liabilities Liabilities, Current [Abstract] Current liabilities: Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Maximum [Member] Maximum [Member] Money Market Funds [Member] Money Market Funds [Member] Net Cash Provided by (Used in) Financing Activities, Continuing Operations Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Financing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Investing activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Operating activities Net Income (Loss) Attributable to Parent Net loss Net loss Net Income (Loss) Attributable to Parent [Abstract] Numerator: New Accounting Pronouncements, Policy [Policy Text Block] Recent Accounting Pronouncements Nonoperating Income (Expense) Other income, net Number of Operating Segments Number of operating segments Operating Expenses Total operating expenses Operating Expenses [Abstract] Operating expenses: Operating Income (Loss) Loss from operations Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Organization and Basis of Presentation Other Assets, Noncurrent Other assets Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Unrealized gain on available-for-sale securities, net of tax Other Liabilities, Current Other Other Liabilities, Noncurrent Other long-term liabilities Payables and Accruals [Abstract] Payables and Accruals [Abstract] Payments to Acquire Property, Plant, and Equipment Purchases of property and equipment Payments to Acquire Short-term Investments Purchases of short-term investments Performance based restricted stock units. Performance Based Restricted Stock Units [Member] Performance-Based Restricted Stock Units (PSRUs) [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Preferred Stock, Par or Stated Value Per Share Preferred stock, par value Preferred Stock, Shares Authorized Preferred stock, shares authorized Preferred Stock, Shares Issued Preferred stock, shares issued Preferred Stock, Shares Outstanding Preferred stock, shares outstanding Preferred Stock, Value, Issued Preferred stock, $0.0001 par value; 5,000,000 shares authorized as of March 31, 2017 and December 31, 2016, respectively; no shares issued and outstanding as of March 31, 2017 and December 31, 2016, respectively. Prepaid Expense and Other Assets, Current Prepaid expenses and other current assets Proceeds from Issuance of Common Stock Proceeds from issuance of common stock, net of issuance costs Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Excluding Stock Options Proceeds from issuance of shares under the ESPP Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Including Stock Options Proceeds from issuance of common stock under stock plans Proceeds from Maturities, Prepayments and Calls of Short-term Investments Proceeds from maturities of short-term investments Proceeds from Sale of Short-term Investments Sales of short-term investments Property, Plant and Equipment, Net Property and equipment, net Range [Axis] Range [Axis] Range [Domain] Range [Domain] Research and Development Expense Research and development Research and Development Expense [Member] Research and Development [Member] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Restricted Stock Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] Retained Earnings (Accumulated Deficit) Accumulated deficit Schedule of Accounts Payable and Accrued Liabilities [Table Text Block] Schedule of Accrued Liabilities and Other Liabilities Cash, Cash Equivalents and Investments [Table Text Block] Schedule of Securities Classified as Cash, Cash Equivalents and Short-term Investments Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Computation of Basic and Diluted Loss Per Share Attributable to Common Stockholders Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Summary of Stock-Based Compensation Recognized Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Share-based Compensation Stock-based compensation Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Shares outstanding Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Exercise Price, and Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Exercise Price, and Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Exercise Price, and Additional Disclosures [Abstract] Equity Award [Domain] Equity Award [Domain] Shares Issued, Price Per Share Purchase price of common shares Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Stockholders' Equity Attributable to Parent Total stockholders' equity Stockholders' Equity Attributable to Parent [Abstract] Stockholders' equity: Stockholders' Equity Note Disclosure [Text Block] Stockholders' Equity Stock Issued During Period, Shares, Employee Stock Purchase Plans Shares sold under ESPP Stock Issued During Period, Shares, New Issues Common stock sold and issued Stock Issued During Period, Shares, Restricted Stock Award, Gross Stock issued during period, restricted stock units Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Shares purchased by employees on exercise of options Subsequent Events [Abstract] Subsequent Events [Abstract] Subsequent Events [Text Block] Subsequent Events Trading Symbol Trading Symbol Use of Estimates, Policy [Policy Text Block] Use of Estimates