Statement of Financial Position [Abstract] Preferred stock, par value (in USD per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred stock, shares issued Preferred Stock, Shares Issued Preferred stock, shares outstanding Preferred Stock, Shares Outstanding Common stock, par value (in USD per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares, issued Common Stock, Shares, Issued Common stock, shares, outstanding Common Stock, Shares, Outstanding Revenue Recognition [Abstract] Significant Agreements Long-term Contracts or Programs Disclosure [Text Block] Investments [Abstract] Schedule of Investments [Table] Schedule of Investments [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Certificates of deposit Certificates of Deposit [Member] U.S. Treasury securities US Treasury Securities [Member] Preferred stock of U.S. corporation Preferred Stock [Member] Common Stock Common Stock [Member] Schedule of Investments [Line Items] Schedule of Investments [Line Items] Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Estimated Fair Value Available-for-sale Securities Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Common stock offering, May 27, 2014 Common Stock Offering, May 27, 2014 [Member] Common Stock Offering, May 27, 2014 [Member] Common stock offering, November 5, 2014 Common Stock Offering, November 5, 2014 [Member] Common Stock Offering, November 5, 2014 [Member] Statement [Line Items] Statement [Line Items] New issues of stock during period (in shares) Stock Issued During Period, Shares, New Issues Offering price per share (in USD per share) Shares Issued, Price Per Share Stock issuance costs Payments of Stock Issuance Costs Stockholders' Equity Note [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Employee Employees [Member] Employees [Member] Non-Employee Non-Employee Expense [Member] Non-Employee Expense [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Research and development expense Research and Development Expense [Member] General and administrative expense General and Administrative Expense [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Allocated share-based compensation expense Allocated Share-based Compensation Expense Debt Disclosure [Abstract] Loan Payable Debt Disclosure [Text Block] Accounting Policies [Abstract] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Reclassifications Reclassification, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Investments Investment, Policy [Policy Text Block] Concentration of Credit Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Accounts Receivable Receivables, Policy [Policy Text Block] Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Property and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Impairment of Long-Lived Assets Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Deferred Lease Obligation Lease, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Research and Development Prepaids and Accruals Clinical Trial Accruals [Policy Text Block] The entire policy related to clinical trial accruals. Research and Development Expenses Research and Development Expense, Policy [Policy Text Block] Interest Income (Expense), Net Interest Expense, Policy [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Share-Based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] 401(k) Plan Pension and Other Postretirement Plans, Nonpension Benefits, Policy [Policy Text Block] Basic and Dilutive Net Loss Per Share of Common Stock Earnings Per Share, Policy [Policy Text Block] Segments Segment Reporting, Policy [Policy Text Block] Impact of Recently Issued Accounting Standards and Impact of Recently Adopted Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Income Tax Disclosure [Abstract] Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Components of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Summary of Uncertain Tax Benefit Summary of Income Tax Contingencies [Table Text Block] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Employee stock option Employee Stock Option [Member] Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Expected term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Weighted-average risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Weighted-average fair value per option (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Statement of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net loss Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net loss to net cash used in operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation of property and equipment Depreciation Amortization of debt costs Amortization of Debt Issuance Costs Amortization of premium/discount on investments Accretion (Amortization) of Discounts and Premiums, Investments Share-based compensation Share-based Compensation Amortization of lease-related obligations Increase (Decrease) in Deferred Liabilities Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Accounts payable and accrued liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Purchases of short-term investments Payments to Acquire Short-term Investments Purchases of long-term investments Payments to Acquire Long-term Investments Sales of short-term investments Proceeds from Sale of Short-term Investments Maturities of short-term investments Proceeds from Maturities, Prepayments and Calls of Short-term Investments Maturities of long-term investments Proceeds from Maturities, Prepayments and Calls of Long-term Investments Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from exercise of stock options Proceeds from Stock Options Exercised Proceeds from employee stock purchase plan stock purchases Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Excluding Stock Options Proceeds from exercise of warrants Proceeds from Warrant Exercises Proceeds from public offerings, net of offering costs Proceeds from Issuance of Common Stock Payments for deferred financing costs Proceeds from (Payments for) Other Financing Activities Repayments of debt Repayments of Debt Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Beginning of period Cash and Cash Equivalents, at Carrying Value End of period Supplemental disclosure of cash flow information Supplemental Cash Flow Information [Abstract] Cash paid for interest Interest Paid, Net Non-cash acquisition of investment in U.S. corporation Noncash or Part Noncash Acquisition, Investments Acquired Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Exercise Price Range [Axis] Exercise Price Range [Axis] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Exercise price range, $1.53 to 7.57 Exercise Price Range, $1.53 to 7.57 [Member] Exercise Price Range, $1.53 to 7.57 Exercise Price Range, $7.58 to 8.06 Exercise Price Range, $7.58 to 8.06 [Member] Exercise Price Range, $7.58 to 8.06 Exercise Price Range, $15.79 to 18.75 Exercise Price Range, $15.79 to 18.75 [Member] Exercise Price Range, $15.79 to 18.75 Exercise Price Range, $18.76 to 39.17 Exercise Price Range, $18.76 to 39.17 [Member] Exercise Price Range, $18.76 to 39.17 Exercise Price Range, $39.18 to 53.74 Exercise Price Range, $39.18 to 53.74 [Member] Exercise Price Range, $39.18 to 53.74 Exercise Price Range, $1.53 to 53.74 Exercise Price Range, $1.53 to 53.74 [Member] Exercise Price Range, $1.53 to 53.74 Share-based compensation, number of outstanding options (in shares) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options Share-based compensation, outstanding options, weighted average remaining contractual term Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term Share-based compensation, outstanding options, weighted average exercise price (in USD per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price Share-based compensation, number of exercisable options (in shares) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options Share-based compensation, exercisable options, weighted average exercise price (in USD per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price Share-based compensation, lower range limit (in USD per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit Share-based compensation, upper range limit (in USD per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit Selected Quarterly Financial Information [Abstract] Selected Quarterly Financial Data (Unaudited) Quarterly Financial Information [Text Block] Effective Income Tax Rate Reconciliation, Amount [Abstract] Effective Income Tax Rate Reconciliation, Amount [Abstract] Income tax benefit at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount State income taxes Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Research and development credits Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount Foreign rate differential Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount Permanent items Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount Provision to return adjustments Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Effect of change in state tax rate Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount Increase in unrecognized tax benefits Effective Income Tax Reconciliation Increase Due to Unrecognized Tax Benefits Effective income tax reconciliation increase due to unrecognized tax benefits. Change in valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Net benefit Income Tax Expense (Benefit) Effective Income Tax Rate Reconciliation, Percent [Abstract] Effective Income Tax Rate Reconciliation, Percent [Abstract] Income tax benefit at statutory rate, tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent State income taxes, tax rate Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Research and development credits, tax rate Effective Income Tax Rate Reconciliation, Tax Credit, Research, Percent Foreign rate differential, tax rate Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent Permanent items, tax rate Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent Provision to return adjustments, tax rate Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effect of change in state tax rate, tax rate Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent Increase in unrecognized tax benefits, tax rate Effective Income Tax Reconciliation Increase Due to Unrecognized Tax Benefits Tax Rate Effective income tax reconciliation increase due to unrecognized tax benefits, tax rate. Change in valuation allowance, tax rate Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Net benefit, tax rate Effective Income Tax Rate Reconciliation, Percent Line of Credit Facility [Table] Line of Credit Facility [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] First tranche First Tranche [Member] First Tranche [Member]. Second tranche Second Tranche [Member] Second Tranche [Member]. Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Loan and security agreement, maximum capacity Line of Credit Facility, Maximum Borrowing Capacity Interest only period Interest Only Period Interest only period. Principal and interest amortization period Principal And Interest Amortization Period Principal and interest amortization period. Loan and security agreement, interest rate Line of Credit Facility, Interest Rate During Period Loans payable, current Loans Payable, Current Summary of Short-term and Long-term Investments Available-for-sale Securities [Table Text Block] Summary of Investments with Unrealized Losses, Aggregated by Investment Type and the Length of Time Schedule of Unrealized Loss on Investments [Table Text Block] Summary of the scheduled maturity of Company investments Investments Classified by Contractual Maturity Date [Table Text Block] Long-term Purchase Commitment [Table] Long-term Purchase Commitment [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Value Type [Axis] Value Type [Axis] Value Type [Axis] Value Type [Domain] Value Type [Domain] [Domain] for Value Type [Axis] Stated Value Stated Value [Member] Stated Value [Member] Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Brincidofovir Brincidofovir [Member] Brincidofovir [Member]. Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, Forecast Scenario, Forecast [Member] BARDA Option Segment [Axis] BARDA Option Segment [Axis] BARDA Option Segment [Axis] BARDA Option Segment [Domain] BARDA Option Segment [Domain] [Domain] for BARDA Option Segment [Axis] Second Option Segment Second Option Segment [Member] Second Option Segment [Member] Third Option Segment Third Option Segment [Member] Third Option Segment [Member] Collaborative Arrangements and Non-collaborative Arrangements [Axis] Type of Arrangement and Non-arrangement Transactions [Axis] Collaborative Arrangements and Non-collaborative Arrangement Transactions [Domain] Arrangements and Non-arrangement Transactions [Domain] Regents of University of California Regents Of University Of California [Member] Regents Of University Of California [Member]. BARDA BARDA [Member] BARDA [Member] ContraVir Pharmaceuticals ContraVir Pharmaceuticals [Member] ContraVir Pharmaceuticals [Member] The Regents of the University of Michigan The Regents of the University of Michigan [Member] The Regents of the University of Michigan Long-term Purchase Commitment [Line Items] Long-term Purchase Commitment [Line Items] Milestone payments Milestone Payments Aggregate Payments for certain milestones achieved. Sublicense fee percentage Sublicense Fee Percentage Sublicense fee percentage. Sublicense fee amount payable fee percentage Sublicense Fee Amount Payable Fee Percentage Sublicense fee amount, payable fee percentage. Royalties percentage Royalties Percentage Royalties percentage. Expenses recognized Revenue Recognition, Milestone Method, Expenses Recognized Revenue Recognition, Milestone Method, Expenses Recognized Number of extension periods Number Of Extension Periods The number of extension periods. Reimbursement revenue Reimbursement Revenue Fees and commissions Fees and Commissions, Other Contract revenue Contracts Revenue Number Of Extension Periods Through Which Revenue Has Been Recognized Number Of Extension Periods Through Which Revenue Has Been Recognized Number Of Extension Periods Through Which Revenue Has Been Recognized Shares received as consideration for license agreement Other Significant Noncash Transaction, Shares Received as Consideration Other Significant Noncash Transaction, Shares Received as Consideration Value of shares received as consideration for license agreement Other Significant Noncash Transaction, Value of Consideration Received Future licenses revenue Future Licenses Revenue Future Licenses Revenue License agreement, termination notice period License Agreement, Termination Notice License Agreement, Termination Notice Collaboration and licensing revenue Licenses Revenue Convertible preferred stock, shares issued upon conversion Convertible Preferred Stock, Shares Issued upon Conversion License fees Cost of Services, Licenses and Services Stock issued during period, issued for services Stock Issued During Period, Shares, Issued for Services Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Beginning balance Unrecognized Tax Benefits Increase related to current year tax positions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Increase related to prior periods Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Ending balance Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive Gain (Loss) AOCI Attributable to Parent [Member] Accumulated Deficit Retained Earnings [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance Stockholders' Equity Attributable to Parent Share-based compensation Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Exercise of warrants Adjustments to Additional Paid in Capital, Warrant Issued Employee stock purchase plan purchases Stock Issued During Period, Value, Employee Stock Purchase Plan Issuance of common stock, value Stock Issued During Period, Value, New Issues Comprehensive loss: Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Unrealized gain (loss) on investments, net Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Net loss Comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Ending Balance The Business and Summary of Significant Accounting Policies Basis of Presentation and Significant Accounting Policies [Text Block] Income Statement [Abstract] Revenues: Revenues [Abstract] Total revenues Revenues Operating expenses: Operating Expenses [Abstract] Research and development Research and Development Expense General and administrative General and Administrative Expense Total operating expenses Operating Expenses Loss from operations Operating Income (Loss) Other income (expense): Other Nonrecurring (Income) Expense [Abstract] Interest income (expense), net Interest Income (Expense), Net Net loss Other comprehensive loss: Other Comprehensive Income (Loss), Tax [Abstract] Per share information: Earnings Per Share [Abstract] Net loss, basic and diluted (in USD per share) Earnings Per Share, Basic and Diluted Weighted-average shares outstanding, basic and diluted (in shares) Weighted Average Number of Shares Outstanding, Basic and Diluted Property, Plant and Equipment [Abstract] Schedule of Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Lab equipment Other Machinery and Equipment [Member] Leasehold improvements Leasehold Improvements [Member] Computer equipment Computer Equipment [Member] Office furniture and equipment Furniture and Fixtures [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property and equipment, gross Property, Plant and Equipment, Gross Less accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property and equipment, net of accumulated depreciation Property, Plant and Equipment, Net Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Total intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Total fair value of shares vested Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value Total revenues Operating loss Net loss per share, basic and diluted (in USD per share) Fair Value, Less than 12 Months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Unrealized Loss, Less than 12 Months Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Fair Value, Greater than 12 Months Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Unrealized Loss, Greater than 12 Months Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Fair Value, Total Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Unrealized Loss, Total Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Number of securities with unrealized losses, Less than 12 Months Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year Number of securities with unrealized losses, Greater than 12 Months Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year Number of securities with unrealized losses, Total Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Nonrecurring Fair Value, Measurements, Nonrecurring [Member] Class of Stock [Line Items] Class of Stock [Line Items] Fair Value of Financial Instruments Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Other than temporary impairment losses, investments Other than Temporary Impairment Losses, Investments, Available-for-sale Securities Fair value inputs, discount for lack of marketability Fair Value Inputs, Discount for Lack of Marketability Fair value assumptions, exercise price (in USD per share) Fair Value Assumptions, Exercise Price Fair value assumptions, expected dividend rate Fair Value Assumptions, Expected Dividend Rate Fair value assumptions, expected term Fair Value Assumptions, Expected Term Fair value assumptions, risk free interest rate Fair Value Assumptions, Risk Free Interest Rate Fair value assumptions, expected volatility rate Fair Value Assumptions, Expected Volatility Rate Fair value adjustments, assets Assets, Fair Value Adjustment Fair value adjustments, liabilities Liabilities, Fair Value Adjustment Property and Equipment Property and Equipment Property And Equipment [Abstract]. Property and equipment, useful life Property, Plant and Equipment, Useful Life Property and equipment, useful life, leasehold improvements Property, Plant and Equipment, Estimated Useful Lives Impairment of long-lived assets Impairment of Long-Lived Assets Held-for-use Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract] Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract] Defined contribution plan, cost recognized Defined Contribution Plan, Cost Recognized Anti-dilutive securities excluded from the calculation loss per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Segments Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract] Number of operating segments Number of Operating Segments Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Revenue from grants Revenue from Grants Prior period reclassification adjustments Prior Period Reclassification Adjustment Income tax expense (benefit) Income Taxes Income Tax Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] Area of sublease property Operating Leases, Area of Sublease Property Operating Leases, Area of Sublease Property Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Minimum Sublease Rental Payment, 2017 Operating Leases, Future Minimum Payments Due Current, Future Minimum Sublease Rentals Operating Leases, Future Minimum Payments Due Current, Future Minimum Sublease Rentals Minimum Sublease Rental Payment, 2018 Operating Leases, Future Minimum Payments Due In Two Years, Future Minimum Sublease Rentals Operating Leases, Future Minimum Payments Due In Two Years, Future Minimum Sublease Rentals Minimum Sublease Rental Payment, 2019 Operating Leases, Future Minimum Payments Due In Three Years, Future Minimum Sublease Rentals Operating Leases, Future Minimum Payments Due In Three Years, Future Minimum Sublease Rentals Minimum Sublease Rental Payment, 2020 Operating Leases, Future Minimum Payments Due In Four Years, Future Minimum Sublease Rentals Operating Leases, Future Minimum Payments Due In Four Years, Future Minimum Sublease Rentals Minimum Sublease Rental Payment, 2021 Operating Leases, Future Minimum Payments Due In Five Years, Future Minimum Sublease Rentals Operating Leases, Future Minimum Payments Due In Five Years, Future Minimum Sublease Rentals Total future minimum sublease rental payments Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals Schedule of Fair Value of Separate Accounts by Major Category of Investment [Table] Schedule of Fair Value of Separate Accounts by Major Category of Investment [Table] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items] Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning of period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Investment acquired Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Fair value increase/decrease recorded in other comprehensive loss Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Ending of period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Minimum Rental Payment, 2017 Operating Leases, Future Minimum Payments Due, Next Twelve Months Minimum Rental Payment, 2018 Operating Leases, Future Minimum Payments, Due in Two Years Minimum Rental Payment, 2019 Operating Leases, Future Minimum Payments, Due in Three Years Minimum Rental Payment, 2020 Operating Leases, Future Minimum Payments, Due in Four Years Minimum Rental Payment, 2021 Operating Leases, Future Minimum Payments, Due in Five Years Total future minimum rental payments Operating Leases, Future Minimum Payments Due Prepaid research and development expenses Prepaid Development Expenses Prepaid development expenses. Interest receivable Interest Receivable Prepaid insurance Prepaid Insurance Other prepaid expenses and current assets Other Assets, Current Total prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Warrant Warrant [Member] Equity Award [Domain] Restricted stock units (RSUs) Restricted Stock Units (RSUs) [Member] The 2013 Plan The 2013 Plan [Member] The 2013 Plan [Member] The 2013 Employee Stock Purchase Plan The 2013 Employee Stock Purchase Plan [Member] The 2013 Employee Stock Purchase Plan Member. Shares reserved for future issuance Common Stock, Capital Shares Reserved for Future Issuance Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Domestic tax authority Domestic Tax Authority [Member] State and local jurisdiction State and Local Jurisdiction [Member] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Operating loss carryforwards Operating Loss Carryforwards Tax credit carryforward Tax Credit Carryforward, Amount Undistributed earnings of foreign subsidiary Undistributed Earnings of Foreign Subsidiaries Annual limitation of operating loss carryforwards Operating Loss Carryforward, Annual Limitations Operating Loss Carryforward, Annual Limitations Loss limitation ownership change benchmark amount Loss Limitation Ownership Change Benchmark Loss limitation ownership change benchmark amount in regards to any losses incurred prior to such date. Unrecognized tax benefits, gross Penalties and interest accrued Income Tax Examination, Penalties and Interest Accrued Unrecognized tax benefits that would impact effective tax rate Unrecognized Tax Benefits that Would Impact Effective Tax Rate Fair value, measurements, recurring Fair Value, Measurements, Recurring [Member] Money market funds Money Market Funds [Member] Commercial paper Commercial Paper [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Redemption Restriction Period Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Redemption Restriction Period Cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Short-term investments, available-for-sale Available-for-sale Securities, Current Long-term investments Available-for-sale Securities, Noncurrent Total assets Assets, Fair Value Disclosure Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Series F Series F Preferred Stock [Member] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] IPO IPO [Member] Over-allotment option Over-Allotment Option [Member] The 2012 Plan The 2012 Plan [Member] The 2012 Plan [Member] Warrants, outstanding (in shares) Class of Warrant or Right, Outstanding Warrants to purchase common stock (in shares) Class of Warrant or Right, Number of Securities Called by Warrants or Rights Number of shares authorized to be granted Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Share-based compensation, granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Share-based compensation, equity increase Share-Based Compensation, Evergreen Option Provision, Equity Increase Share-Based Compensation, Evergreen Option Provision, Equity Increase Share-based compensation, nonvested awards, compensation not yet recognized, stock options Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options Unrecognized compensation costs, period of recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Number of shares authorized, increase amount Increase (Decrease) in Number of Shares Authorized Increase (decrease) in number of shares authorized. Number of additional shares authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Number of shares available for grant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Share-based compensation, maximum employee subscription rate Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate Discount from market price, entry date Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Offering Date Discount from market price, purchase date Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date Employee stock purchase plan, participation period Employee Stock Purchase Plan, Participation Period Employee Stock Purchase Plan, Participation Period Employee stock purchase plan, automatic reset participation period Employee Stock Purchase Plan, Automatic Reset Participation Period Employee Stock Purchase Plan, Automatic Reset Participation Period Shares issued during period, employee stock purchase plans Stock Issued During Period, Shares, Employee Stock Purchase Plans Employees' contribution liabilities, ESPP Accrued Liabilities, Current Share-based compensation, cash received from exercise of stock options Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options Warrant strike price (in USD per share) Class of Warrant or Right, Exercise Price of Warrants or Rights Tax Benefit from share-based payment arrangements Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Number of options outstanding, Beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Number of options outstanding, Granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Number of options outstanding, Exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Number of options outstanding, Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Number of options outstanding, Ending balance Number of options outstanding, Exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number Number of options outstanding, Vested and expected to vest Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Weighted-average exercise price, Beginning balance (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Weighted-average exercise price, Granted (in USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Weighted-average exercise price, Exercised (in USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Weighted-average exercise price, Forfeited (in USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Weighted-average exercise price, Ending balance (in USD per share) Weighted-average exercise price, Exercisable (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price Weighted-average exercise price, Vested or expected to vest (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Weighted-average remaining contractual life (in years), Beginning Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Weighted-average remaining contractual life (in years), Exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Weighted-average remaining contractual life (in years), Vested or expected to vest Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Aggregate intrinsic value of options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Aggregate intrinsic value of options exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Aggregate intrinsic value of options vested or expected to vest Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Entity Voluntary Filers Entity Voluntary Filers Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Current Reporting Status Entity Current Reporting Status Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Public Float Entity Public Float Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Maturing in one year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value Maturing after one year through two years Available-for-sale Securities, Debt Maturities, Year Two, Fair Value Available-for-sale Securities, Debt Maturities, Year Two, Fair Value Total debt investments Available-for-sale Securities, Debt Securities Total investments Assets and Liabilities Measured at Fair Value on a Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of Prepaid and Other Current Assets Schedule Of Prepaid Expenses And Other Current Assets [Table Text Block] Schedule of prepaid expenses and other current assets [Table TextBlock]. Schedule of Accrued Liabilities Schedule of Accrued Liabilities [Table Text Block] Stockholders' Equity (Deficit) Stockholders' Equity Note Disclosure [Text Block] Expected volatility, ESPP purchase rights Expected term (in years), ESPP purchase rights Weighted-average risk-free interest rate, ESPP purchase rights Expected dividend yield, ESPP purchase rights Weighted-average fair value per option (in USD per share), ESPP purchase rights Executive Officer Executive Officer [Member] Non-executive Non-executive [Member] Non-executive Class of warrant or right, number of securities called by warrants or rights (in shares) Award requisite service period Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period Number of Restricted Stock Units Outstanding Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Beginning Balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Shares issuance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures Ending Balance (in shares) Weighted-Average Grant-Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Granted (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Shares issuance (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value Forfeited (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Nonvested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Accrued compensation Accrued Salaries Accrued research and development expenses Accrued Development Liabilities Accrued development liabilities. Other accrued liabilities Other Accrued Liabilities, Current Total accrued liabilities Schedule of Quarterly Financial Information Quarterly Financial Information [Table Text Block] Operating leases, rent expense Operating Leases, Rent Expense, Net Provision for refundable amount for federal research contract funds Provision for Refundable Amount for Federal Research Contract Funds Provision for Refundable Amount for Federal Research Contract Funds Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Deferred tax assets: Deferred Tax Assets, Gross [Abstract] Domestic net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards, Domestic Foreign net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards, Foreign Research and development expenses Deferred Tax Assets Tax Deferred Expense, Research and Development Deferred Tax Assets Tax Deferred Expense, Research and Development. Capitalized Section 174 expenses Deferred Tax Assets, Tax Deferred Expense, Other Research and development credits Deferred Tax Assets, Tax Credit Carryforwards, Research Accrued bonuses Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Bonuses Share-based compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Other Deferred Tax Assets, Other Total gross deferred tax assets Deferred Tax Assets, Gross Valuation allowance Deferred Tax Assets, Valuation Allowance Total deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Deferred tax liabilities: Deferred Tax Liabilities, Gross [Abstract] Other Deferred Tax Liabilities, Other Total deferred tax liabilities Deferred Tax Liabilities, Gross Total deferred tax assets and liabilities, net Deferred Tax Assets, Net Schedule of Shares Reserved for Future Issuance Schedule of shares reserved for future issuance [Table Text Block] Schedule of shares reserved for future issuance [Table Text Block] Schedule of Fair Value Assumptions, Stock Options Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Summary of Activity Related to Stock Options Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of Other Information Regarding Stock Options Schedule of Other Information Regarding Stock Options [Table Text Block] [Table Text Block] for Schedule of Other Information Regarding Stock Options [Table] Schedule of Share-based Compensation, Shares Authorized Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] Schedule of Fair Value Assumptions, Employee Stock Purchase Plan Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block] Summary of Activity Related to Restricted Stock Units Schedule of Unvested Restricted Stock Units Roll Forward [Table Text Block] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Schedule of Future Minimum Rental Payments for Operating Leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Summary of Property and Equipment, net Property, Plant and Equipment [Table Text Block] Property and Equipment Property, Plant and Equipment Disclosure [Text Block] ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Accounts receivable Accounts Receivable, Net, Current Prepaid expenses and other current assets Total current assets Assets, Current Property and equipment, net of accumulated depreciation Other long-term assets Other Assets, Noncurrent Total assets Assets LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued liabilities Total current liabilities Liabilities, Current Lease-related obligations Deferred Rent Credit, Noncurrent Total liabilities Liabilities Stockholders’ equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred stock, $0.001 par value, 10,000,000 shares authorized at December 31, 2016 and 2015; no shares issued and outstanding as of December 31, 2016 and 2015 Preferred Stock, Value, Outstanding Common stock, $0.001 par value; 200,000,000 shares authorized at December 31, 2016 and 2015; 46,522,475 and 46,162,525 shares issued and outstanding at December 31, 2016 and 2015, respectively Common Stock, Value, Outstanding Additional paid-in capital Additional Paid in Capital Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated deficit Retained Earnings (Accumulated Deficit) Total stockholders’ equity Total liabilities and stockholders’ equity Liabilities and Equity Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block]