Area of leased property Area of Real Estate Property Document Type Document Type Other expense, net Other Nonoperating Income (Expense) Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Accrued expenses Accrued Expenses Current Accrued expenses current. 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Funded percentage of global development costs Research And Development Collaboration Agreement, Global Development Costs, Funded Percentage Research And Development Collaboration Agreement, Global Development Costs, Funded Percentage Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Entity Address, State or Province Entity Address, State or Province Options to Purchase Common Stock Options To Purchase Common Stock [Member] Options to purchase common stock. Amount of additional fund received for research activities Amount Of Additional Fund Received For Research Activities Amount of additional fund received for research activities Accounts payable Accounts Payable, Current Accumulated deficit Accumulated deficit Retained Earnings (Accumulated Deficit) Options cancelled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Cancelled in Period Share-based Compensation Arrangement by Share-based Payment Award, Options, Cancelled in Period Beginning balance (in shares) Ending balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Summary of significant accounting policies. Common stock options outstanding Common Stock Options Outstanding [Member] Common stock options outstanding. Customer Customer [Axis] Beginning balance (in shares) Ending balance (in shares) Shares, Outstanding Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding as of June 30, 2021 and December 31, 2020, respectively Preferred Stock, Value, Issued Income Taxes Income Tax, Policy [Policy Text Block] Total operating expenses Operating Expenses Exercisable (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Merck Sharp & Dohme Corp Merck Sharp And Dohme Corporation [Member] Merck Sharp and Dohme Corporation. Common stock, par value (in shares) Common Stock, Par or Stated Value Per Share Other comprehensive income, net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Issuance of common stock to participants in 401(k) plan Stock Issued During Period, Value, Employee Benefit Plan Stock-based compensation expense APIC, Share-based Payment Arrangement, Increase for Cost Recognition Related party revenue Collaboration and license revenue Revenue from Contract with Customer, Excluding Assessed Tax Measurement Frequency [Domain] Measurement Frequency [Domain] Share price (in dollars per share) Share Price Deferred rent Increase (Decrease) in Prepaid Rent Percentage of revenue Concentration Risk, Percentage Estimated Useful Life of Asset Schedule Of Estimated Useful Life Of Asset Table [Table Text Block] Schedule of estimated useful life of asset. Geographical [Domain] Geographical [Domain] Statement [Line Items] Statement [Line Items] Potentially Dilutive Securities Not Included in the Diluted Net Loss Per Share Calculations Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Forecast Forecast [Member] Manufacturing costs Accrued Manufacturing Costs Current Accrued Manufacturing costs current. Computer equipment Computer Equipment [Member] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Statement [Table] Statement [Table] Statistical Measurement [Axis] Statistical Measurement [Axis] Credit Facility [Axis] Credit Facility [Axis] Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued U.S. government agencies securities US Government Agencies Debt Securities [Member] Laboratory equipment and office furniture Laboratory Equipment And Office Furniture [Member] Laboratory equipment and office furniture. Marketable Securities Marketable Securities, Policy [Policy Text Block] Entity Small Business Entity Small Business Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Exercisable, weighted average remaining contractual life Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Collaboration Agreement Collaborative Arrangement [Member] Proceeds from follow on offering, net Proceeds from Issuance of Common Stock Amendment Flag Amendment Flag Computation of Net Loss Per Common Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Total Operating Leases, Future Minimum Payments Due 2021 Operating Leases, Future Minimum Payments, Remainder of Fiscal Year Research and Development Research and Development Expense, Policy [Policy Text Block] Balance Sheet Components Supplemental Balance Sheet Disclosures [Text Block] Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Entity Central Index Key Entity Central Index Key Measurement Frequency [Axis] Measurement Frequency [Axis] Merck Merck [Member] Merck. Issuance of common stock under 401(k) Plan (in shares) Stock Issued During Period, Shares, Employee Benefit Plan Deferred rent, current Deferred Rent Credit, Current Financial Instruments [Domain] Financial Instruments [Domain] Geographical [Axis] Geographical [Axis] Vested and expected to vest, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Intrinsic Value Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Gross Unrealized Gain Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Cash on deposit with banks Interest-bearing Deposits in Banks and Other Financial Institutions Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] ESPP 401(k) Matching Plan Employee Stock [Member] Income Statement Location [Axis] Income Statement Location [Axis] Common stock options available for grant Common Stock Options Available For Grant [Member] Common stock options available for grant. Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Income Statement Location [Domain] Income Statement Location [Domain] Cash flows from financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Summary of Cash and Cash Equivalents and Marketable Securities Classified as Available-for-sale Securities Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Collaborative arrangement funding, amount Collaborative Arrangement Annual Funding Amount Over Agreement Term Collaborative arrangement annual funding amount over agreement term. Number of options to extend performance of research program Number Of Options To Extend Performance Of Research Program Number of options to extend performance of research program. Capitalized Contract Cost [Domain] Capitalized Contract Cost [Domain] Other non-current assets Other Assets, Noncurrent Issuance of common stock under offering, net of issuance costs Stock Issued During Period, Value, New Issues Total assets Assets Scenario [Axis] Scenario [Axis] Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Summary of significant accounting policies Title of 12(b) Security Title of 12(b) Security Accrued Liabilities Schedule of Accrued Liabilities [Table Text Block] Weighted-average grant date fair value of stock options, granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value ESPP shares available for purchase Four Zero One K Matching Plan [Member] Four zero one k matching plan. Antidilutive Securities Antidilutive Securities [Axis] Concentration of Credit and Other Risks Concentration Risk, Credit Risk, Policy [Policy Text Block] Stock repurchase plan, authorized (in shares) Stock Repurchase Program, Number of Shares Authorized to be Repurchased Aggregate net proceeds Sale of Stock, Consideration Received on Transaction Short-term marketable securities Short-term Investments [Member] Total accrued liabilities Accrued Liabilities Total liabilities Liabilities Schedule of Shares of Common Stock Reserved for Issuance Schedule of Stock by Class [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Proceeds from employee stock purchase plan Proceeds, Issuance of Shares, Share-based Payment Arrangement, Excluding Option Exercised Level 1 Fair Value, Inputs, Level 1 [Member] Options cancelled (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Cancelled in Period, Weighted Average Exercise Price Share-based Compensation Arrangements by Share-based Payment Award, Options, Cancelled in Period, Weighted Average Exercise Price Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Accounts payable Increase (Decrease) in Accounts Payable Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding Aggregate offering price Sale of Stock, Aggregate Offering Price Sale of Stock, Aggregate Offering Price Clinical Development Event [Axis] Clinical Development Event [Axis] Clinical Development Event Additional Paid-In Capital Additional Paid-in Capital [Member] Antidilutive Securities, Name Antidilutive Securities, Name [Domain] Capitalized Contract Cost [Axis] Capitalized Contract Cost [Axis] Class of Stock [Line Items] Class of Stock [Line Items] Japan JAPAN Clinical trials and research and development costs Accrued Clinical Trials And Research And Development Costs Current Accrued clinical trials and research and development costs current. Asset Class [Axis] Asset Class [Axis] 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] Number of marketable securities in unrealized loss positions less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] R&D tail period Research And Development Service Tail Period Research And Development Service Tail Period Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Research and development Research and Development Expense Beginning balance (in dollars per share) Ending balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Number of purchase periods Number Of Purchase Periods Number of purchase periods. Comprehensive Loss Comprehensive Income, Policy [Policy Text Block] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Concentration Risk Type Concentration Risk Type [Axis] Total property and equipment, gross Property, Plant and Equipment, Gross Proceeds from exercise of stock options Proceeds from Stock Options Exercised First Indication First Indication [Member] First indication. Collaborative Arrangement [Line Items] Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Vesting of common stock from early exercises Vesting Of Common Stock From Early Exercises Vesting of common stock from early exercises. Income Statement [Abstract] Income Statement [Abstract] Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Deferred rent, non-current Deferred Rent Credit, Noncurrent Stock options, early exercise, repurchase period Share-Based Compensation Arrangement By Share-based Payment Award, Options, Early Exercise Repurchase Period Share-Based Compensation Arrangement By Share-based Payment Award, Options, Early Exercise Repurchase Period Use of Estimates Use of Estimates, Policy [Policy Text Block] Current assets: Assets, Current [Abstract] Remaining extension term Research And Development Option Remaining Extension Term Research And Development Option Remaining Extension Term Total comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Scenario [Domain] Scenario [Domain] Counterparty Name [Domain] Counterparty Name [Domain] City Area Code City Area Code Document Period End Date Document Period End Date Related party receivable from collaboration Due from Related Parties, Current Total Common Stock, Capital Shares Reserved for Future Issuance Net loss Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Letter of credit as a security deposit Security Deposit Impairment of Long-Lived Assets Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Operating lease term Lessee, Operating Lease, Term of Contract Proof-Of-Concept Trial, CVM Research Proof-Of-Concept Trial, CVM Research Program [Member] Proof-Of-Concept Trial, CVM Research Program Stock-based compensation expense Share-based Payment Arrangement, Noncash Expense Vesting of common stock from early exercises Stock Issued During Period Value Vesting Of Early Exercised Stock Options Stock issued during period value vesting of early exercised stock options. Cover [Abstract] Cover [Abstract] Vested and expected to vest (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Weighted Average Exercise Price Estimated useful life of asset Property, Plant and Equipment, Useful Life Tenant improvement allowances Tenant Improvements Contract liabilities Increase (Decrease) in Contract with Customer, Liability Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Amortization of premium (discount) on marketable securities Accretion (Amortization) of Discounts and Premiums, Investments Concentration Risk Benchmark Concentration Risk Benchmark [Axis] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Fair Value Debt Securities, Available-for-sale Equity Components Equity Components [Axis] Second Indication Second Indication [Member] Second indication. Minimum Minimum Minimum [Member] Reserve balance for Sales Agreement Reverse Balance For Sales Agreement [Member] Reverse Balance For Sales Agreement Entity Interactive Data Current Entity Interactive Data Current United States UNITED STATES Corporate and agency bonds Corporate Bond Securities [Member] Options exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Schedule of Reconciliation of Cash, Cash Equivalent and Restricted Cash Restrictions on Cash and Cash Equivalents [Table Text Block] Fair Value Measurements Fair Value Disclosures [Text Block] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Stockholders' Equity Stockholders' Equity Note Disclosure [Text Block] Summary of Activity under 2008 Plan and 2018 Plan Share-based Payment Arrangement, Option, Activity [Table Text Block] Stock-Based Compensation Share-based Payment Arrangement [Policy Text Block] Customer Customer [Domain] Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] Net purchase of property and equipment Payments to Acquire Machinery and Equipment Additional paid-in capital Additional Paid in Capital, Common Stock Entity Registrant Name Entity Registrant Name Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Assets: Assets, Fair Value Disclosure [Abstract] Reduction in related party contract asset due to Amended Collaboration Agreement with Merck Increase (Decrease) in Due From Related Parties, Contract Assets, Noncash Increase (Decrease) in Due From Related Parties, Contract Assets, Noncash Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Research and development Research and Development Expense [Member] Vesting of common stock from early exercises (in shares) Stock Issued During Period Shares Vesting Of Early Exercised Stock Options Stock issued during period shares vesting of early exercised stock options. Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Restricted cash Restricted Cash, Noncurrent Gross Unrealized Loss Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Options granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Excluding Shares Issued in Connection with Acquisition, Weighted Average Exercise Price Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Excluding Shares Issued in Connection with Acquisition, Weighted Average Exercise Price Foreign Currency Transactions Foreign Currency Transactions and Translations Policy [Policy Text Block] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Document Transition Report Document Transition Report Title of Individual [Axis] Title of Individual [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Numerator: Net Income (Loss) Attributable to Parent [Abstract] Duration of each purchase period Duration Of Each Purchase Period Duration of each purchase period. Level 2 Fair Value, Inputs, Level 2 [Member] Option exercise fee Research And Development, Option Exercise Fee Research And Development, Option Exercise Fee Document Quarterly Report Document Quarterly Report Asset Class [Domain] Asset Class [Domain] General and administrative General and Administrative Expense [Member] Equity [Abstract] Equity [Abstract] Fair value of financial assets Assets, Fair Value Disclosure Research collaboration and license agreements extension fee Research Collaboration And License Agreements Extension Fee Research collaboration and license agreements extension fee. Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Contract liabilities Contract with Customer, Liability, Current Customer Concentration Risk Customer Concentration Risk [Member] Credit Facility [Domain] Credit Facility [Domain] Weighted average shares used to compute net loss per share, diluted (in shares) Weighted average number of shares used in computing net loss per share, diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Letter of Credit Letter of Credit [Member] Net loss per share, basic (in dollars per share) Earnings Per Share, Basic Number of operating business segment Number of Operating Segments Entity File Number Entity File Number Research and development performance obligation period Research And Development Performance Obligation Period Research And Development Performance Obligation Period Public Stock Offering Public Stock Offering [Member] Public Stock Offering Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Remaining extension fee Research Collaboration And License Agreements Remaining Extension Fee Research Collaboration And License Agreements Remaining Extension Fee Transaction price for the two-year performance obligation Revenue, Remaining Performance Obligation, Amount Share-based compensation expense Total stock-based compensation expense Share-based Payment Arrangement, Expense Issuance of common stock under employee stock purchase plan Stock Issued During Period, Value, Employee Stock Purchase Plan Counterparty Name [Axis] Counterparty Name [Axis] Denominator: Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract] Common stock, $0.001 par value; 400,000,000 shares authorized; 77,307,156 and 70,585,364 shares issued and outstanding as of June 30, 2021 and December 31, 2020, respectively Common Stock, Value, Issued Document Fiscal Year Focus Document Fiscal Year Focus Milestone payments Eligible Milestone Payments Receivable Eligible milestone payments receivable. Commercial paper Commercial Paper [Member] Exercisable, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Property Subject to or Available for Operating Lease, by Major Property Class [Table] Property Subject to or Available for Operating Lease, by Major Property Class [Table] Entity Current Reporting Status Entity Current Reporting Status Third Indication Third Indication [Member] Third indication. Required amount to expend Amount Of Fund Received For Research Activities, Required Expendable Amount Amount Of Fund Received For Research Activities, Required Expendable Amount Related Party Transaction [Axis] Related Party Transaction [Axis] Net Loss per Share Earnings Per Share, Policy [Policy Text Block] Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Related party contract asset Increase (Decrease) in Contract with Customer, Asset Vested and expected to vest (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Number of Shares Research Collaboration and License Agreements Collaborative Arrangement Disclosure [Text Block] Cash flows from investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Common stock, shares issued (in shares) Common Stock, Shares, Issued Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value 2022 Operating Leases, Future Minimum Payments, Year One Operating Leases, Future Minimum Payments, Year One Personnel-related costs Accrued Personnel Expense Current Accrued personnel expense current. Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Total stockholders' equity Beginning balance Ending balance Stockholders' Equity Attributable to Parent Deferred offering costs paid Payments of Stock Issuance Costs Concentration Risk Type Concentration Risk Type [Domain] Upfront license fee Upfront License Fee Upfront license fee. Rent expense Operating Leases, Rent Expense, Net Clinical Development Event [Domain] Clinical Development Event [Domain] Clinical Development Event [Domain] Total liabilities and stockholders' equity Liabilities and Equity Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Income Taxes Income Tax Disclosure [Text Block] Entity Address, City or Town Entity Address, City or Town Milestone payment for potential achievement of certain clinical development events Milestone Payment For Potential Achievement Of Certain Clinical Development Events Milestone payment for potential achievement of certain clinical development events. Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Maximum percentage of payroll deductions of employee's compensation Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate General and administrative General and Administrative Expense Financial Instrument [Axis] Financial Instrument [Axis] Potentially dilutive securities not included in calculations of diluted per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Maximum duration for purchase under employee stock purchase plan Offering Period For Purchase Under Employee Stock Purchase Plan Offering period for purchase under employee stock purchase plan. Other non-cash expenses Other Noncash Income (Expense) Entity Ex Transition Period Entity Ex Transition Period Equity Component Equity Component [Domain] Cash, cash equivalents and marketable securities Cash, Cash Equivalents, and Short-term Investments Percentage of purchase of common stock fair market value Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Offering Date Net unrealized gain on available-for-sale marketable securities OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Property and equipment, net Total property and equipment, net Total leasehold improvements Property, Plant and Equipment, Net Construction in process Construction in Progress [Member] Performance of R&D services period Research And Development Service Performance Period Research and development service performance period. Entity Tax Identification Number Entity Tax Identification Number Phase 3 Clinical Event Phase 3 Clinical Event [Member] Phase 3 Clinical Event Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Interest income, net Interest Income (Expense), Nonoperating, Net Net loss Net loss Net loss Net Income (Loss) Attributable to Parent Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Common stock remaining to be sold under open market sales agreement Sale of Stock, Common Stock Available For Issuance Sale of Stock, Common Stock Available For Issuance Reinvestment amount from option fee Research And Development, Option Exercise Fee, Reinvestment Amount Research And Development, Option Exercise Fee, Reinvestment Amount Uses and Sources of Liquidity Uses And Sources Of Liquidity, Policy [Policy Text Block] Uses And Sources Of Liquidity, Policy Total current assets Assets, Current Current Fiscal Year End Date Current Fiscal Year End Date Operating expenses: Operating Expenses [Abstract] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Number of Options Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Deferred offering costs accrued but not yet paid Deferred Offering Costs Accrued But Not Yet Paid Deferred offering costs accrued but not yet paid. Document Fiscal Period Focus Document Fiscal Period Focus Reduction in letter of credit Reduction In Security Deposit Reduction in security deposit. Issuance of common stock under employee stock purchase plan (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Entity Filer Category Entity Filer Category Summary of Stock Based Compensation Expense Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Common Stock Common Stock [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Long-Lived Tangible Asset [Domain] Long-Lived Tangible Asset [Domain] Schedule of Milestone Payments by Indications Collaborative Arrangement and Arrangement Other than Collaborative [Table Text Block] Concentration Risk Benchmark Concentration Risk Benchmark [Domain] European Union European Union [Member] Property and Equipment Property, Plant and Equipment [Table Text Block] Issuance of common stock under offering, net of issuance cost (in shares) Number of shares issued in transaction (in shares) Stock Issued During Period, Shares, New Issues Leasehold improvements Leasehold Improvements [Member] Schedule of Recognized Revenue from Collaboration and License Agreements Schedule Of Recognized Revenue From Collaboration And License Arrangements Table [Table Text Block] Schedule of recognized revenue from collaboration and license arrangements. Revenue Revenue Benchmark [Member] Money market funds Money Market Funds [Member] Shares committed under ESPP Share-based Payment Arrangement [Member] Less: accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Related party contract asset Contract with Customer, Asset, after Allowance for Credit Loss, Current Non-cash investing and financing activities: Noncash Investing and Financing Items [Abstract] Issuance of common stock upon exercise of stock options (in shares) Options exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Net (decrease) increase in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Upfront payment received Collaborative Arrangement Up Front Payment Received Collaborative arrangement up front payment received. 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Award Type [Domain] Award Type [Domain] Related party receivable from collaboration Increase (Decrease) in Accounts Receivable, Related Parties Corporate and agency bonds Corporate Debt Securities [Member] Trading Symbol Trading Symbol Related party revenue Related party revenue Revenue from Related Parties Exercisable (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Vested and expected to vest, weighted average remaining contractual life Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Weighted Average Remaining Contractual Term Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested And Expected To Vest, Weighted Average Remaining Contractual Term Additional term Research And Development Option Extend Term Research and development option extend term. 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