Purchases of investments Common stock, $0.00001 par value; 150,000,000 shares authorized and [ ] and 48,251,819 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively Convertible preferred stock, $0.00001 par value; 10,000,000 shares authorized and no shares issued and outstanding at September 30, 2021 and December 31, 2020. Loss contingency claim amount Name of plaintiff Lawsuit filed date Loss Contingency, Estimate of Possible Loss Loss contingency, answer and counterclaims by plaintiff filing date Loss Contingency Answer And Counterclaims By Plaintiff Filing Date Loss contingency, answer and counterclaims by plaintiff filing date. Loss contingency, answer, affirmative defenses and counterclaims filing date Loss Contingency Answer Affirmative Defenses And Counterclaims Filing Date Loss contingency answer, affirmative defenses and counterclaims filing date. Loss Contingency, Name of Plaintiff Loss Contingency, Lawsuit Filing Date Patent Infringement Lawsuit Patent Infringement Lawsuit [Member] Patent infringement lawsuit. Litigation Case [Domain] Litigation Case [Axis] Loss Contingencies [Line Items] Loss Contingencies [Table] Percentage of taxable income from net operating losses for suspension of annual deduction limitation Percentage Of Taxable Income From Net Operating Losses For Suspension Of Annual Deduction Limitation Percentage of taxable income from net operating losses for suspension of annual deduction limitation. Net operating loss carryback Net Operating Loss Carryback Period Net operating loss carryback. Entity Common Stock, Shares Outstanding Document Transition Report Document Quarterly Report Entity Incorporation, State or Country Code Security Exchange Name Title of 12(b) Security Entity Interactive Data Current Local Phone Number City Area Code Entity Address, Postal Zip Code Entity Address, State or Province Entity Address, City or Town First year of lease term. Lease Contractual Term Lease Contractual Term [Domain] Lease Contractual Term Lease Contractual Term [Axis] New Lease Agreement Lease Agreements [Member] Finite-Lived Intangible Assets, Major Class Name Finite Lived Intangible Assets Major Class Name [Domain] Finite-Lived Intangible Assets by Major Class Finite Lived Intangible Assets By Major Class [Axis] Schedule Of Operating Leased Assets [Table] Schedule Of Operating Leased Assets [Table] Stock-based compensation expense Allocated Share Based Compensation Expense Stock-based compensation expense: Share Based Compensation [Abstract] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] General and administrative General And Administrative Expense [Member] Research and development Research And Development Expense [Member] Income Statement Location Income Statement Location [Domain] Income Statement Location Income Statement Location [Axis] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Options exercisable, end of the period Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price Option forfeited/expired Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price Options exercised Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price Options granted Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price Balances, beginning of the period Balances, end of the period Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price Options Outstanding, Weighted-Average Exercise Price Per Share Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price Rollforward Options exercisable, end of the period Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number Option forfeited/expired Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period Options granted Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross Balances, beginning of the period Balances, end of the period Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number Number of Options Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward Underwriting discounts and commissions and offering expenses Payments Of Stock Issuance Costs Common stock price, per share Shares Issued Price Per Share Class Of Stock [Line Items] Class Of Stock [Line Items] Underwriters Over Allotment Option [Member] Underwritten Public Offering Underwritten Public Offering [Member] Underwritten public offering. Sale of Stock Sale Of Stock Name Of Transaction [Domain] Sale of Stock Subsidiary Sale Of Stock [Axis] Schedule Of Stock By Class [Table] Schedule Of Stock By Class [Table] Period granted to underwriters to purchase additional shares Option Period Granted To Underwriters To Purchase Additional Shares Option period granted to underwriters to purchase additional shares. License Agreement [Line Items] Research And Development Arrangement Contract To Perform For Others [Line Items] UCSB University Of California Santa Barbara [Member] University of California, Santa Barbara. Research and Development Arrangement, Contract to Perform for Others, Type Research And Development Arrangement Contract To Perform For Others Type [Domain] Research and Development Arrangement, Contract to Perform for Others, Type Research And Development Arrangement Contract To Perform For Others By Type [Axis] Schedule Of Research And Development Arrangement Contract To Perform For Others [Table] Schedule Of Research And Development Arrangement Contract To Perform For Others [Table] Additional sublicense fees Additional Sublicense Fees Additional sublicense fees. Milestone payment receivable Stock Issued During Period Value Employee Stock Purchase Plan Options exercised Exercise of stock options, shares Stock Issued During Period Shares Stock Options Exercised Exercise of stock options Stock Issued During Period Value Stock Options Exercised Issuance of common stock in follow-on offering, net of issuance costs, shares Stock Issued During Period Shares New Issues Issuance of common stock in follow-on offering, net of issuance costs Stock Issued During Period Value New Issues Beginning balance, shares Ending balance, shares Shares Issued Accumulated Deficit Retained Earnings [Member] Accumulated Other Comprehensive Income/(Loss) Accumulated Other Comprehensive Income [Member] Additional Paid-in Capital Additional Paid In Capital [Member] Common Stock Common Stock [Member] Equity Component Equity Component [Domain] Equity Components Statement Equity Components [Axis] Statement Of Stockholders Equity [Abstract] Comprehensive loss Comprehensive Income Net Of Tax Other comprehensive income (loss) Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax Other comprehensive income (loss): Other Comprehensive Income Loss Tax [Abstract] Shares used to compute net loss per share, basic and diluted Weighted Average Number Of Share Outstanding Basic And Diluted Net loss per share, basic and diluted Income Loss From Continuing Operations Per Basic And Diluted Share Net loss Net income (loss) Net Income Loss Benefit from income taxes Income Tax Expense Benefit Loss before income taxes Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest Other income (expense), net Other Nonoperating Income Expense Interest income Investment Income Interest Loss from operations Operating Income Loss Total operating expenses Operating Expenses General and administrative General And Administrative Expense Research and development Research And Development Expense Operating expenses: Operating Expenses [Abstract] Type of Revenue [Extensible List] Type Of Revenue Extensible List Revenues Revenue recognized from collaborative arrangement Revenue From Contract With Customer Excluding Assessed Tax Statement Of Income And Comprehensive Income [Abstract] Common stock, shares outstanding Common Stock Shares Outstanding Common stock, shares issued Deferred revenue Increase Decrease In Contract With Customer Liability Accounts payable Increase Decrease In Accounts Payable Entity Address, Address Line Two Entity Address, Address Line One Entity Tax Identification Number Entity File Number Entity Shell Company Entity Emerging Growth Company Entity Small Business Entity Filer Category Entity Current Reporting Status Current Fiscal Year End Date Entity Central Index Key Entity Registrant Name Trading Symbol Document Fiscal Period Focus Document Fiscal Year Focus Document Period End Date Amendment Flag Document Type Cover [Abstract] Milestone Payment Receivable Milestone payment receivable. Sublicense fees Sublicense Fees Sublicense fees. Second Target under Discovery Agreement Second Target Under Discovery Agreement [Member] Second target under discovery agreement. First Target under Discovery Agreement First Target Under Discovery Agreement [Member] First target under discovery agreement. Deferred revenue recognition maturity month and year Contract With Customer Liability Maturity Month And Year Contract with customer liability maturity month and year. Deductions Contract With Customer Liability Revenue Recognized Revenue From Contract With Customer [Abstract] Contract With Customer Liability Additions Contract with customer liability additions. Milestone payments payable Milestone Payment Payable Milestone payment payable. Immuno Gen Inc Immuno Gen Inc Immuno Gen Inc [Member] ImmunoGen, Inc. Upfront cash payment Cash Payment To Execute Agreement Cash payment to execute the agreement. Estimated research service termination date Estimated Research Service Termination Date Estimated research service termination date. Upfront payment received Upfront Fee Received Upfront fee received. Total transaction price Aggregate Collaboration Transaction Amount Aggregate collaboration transaction amount. Number of research targets selected Number Of Research Targets Selected Number of research targets selected. Research terms Research And Development Arrangement Contract To Perform For Others Description And Terms Each Of Two Additional Targets Achieving Additional Targets [Member] Achieving additional targets. Times of increments for extended collaboration target research time Increments Of Extended Collaboration Target Research Times Increments of extended collaboration target research times. Extension of research term for each collaboration target Extension Of Research Term For Each Collaboration Target Extension of research term for each collaboration target. Period of nomination of additional target from effective date Period Of Nomination Of Additional Target Period of nomination of additional target. Collaboration target research term Collaboration Target Research Term Collaboration target research term. Number of collaboration target Number Of Collaboration Target Number of collaboration target. Number of oncology target Number Of Oncology Target Number of oncology target. Research and development service fees Research And Development Service Fees Research and development service fees. Additional Contingent Payments Additional Contingent Payments [Member] Additional contingent payments. Right to expand the number of additional collaboration target Right To Expand Number Of Additional Collaboration Target Right to expand the number of additional collaboration target. Contingent payments payable Contingent Payments Payable Upon Achieving Development Regulatory And Commercial Milestones Contingent payments payable upon achieving development regulatory and commercial milestones. Number of additional collaboration target Number Of Additional Collaboration Target Number of additional collaboration target. Percentage share of profit and losses Profit Share Upon Exercise Of Co Development Option Profit share upon exercise of co-development option. Common stock, shares issuable under agreement, price per share Share Price Amgen Other Products Amgen Other Products [Member] Amgen other products. Amgen Products Amgen Products [Member] Amgen products. EGFR Products E G F R Products [Member] EGFR Products. Collaboration and License Agreement Collaboration And License Agreement [Member] Collaboration and license agreement. Estimated premium on the stock sold Estimated Premium On Issuance Of Shares Estimated premium on issuance of shares. Lock-up period for share disposal Lock Up Period For Share Transaction Under Collaboration And License Agreement Lock-up period for share transaction under collaboration and license agreement. Period used to calculate weighted average price per share Period Used To Calculate Weighted Average Price Per Share Period used to calculate weighted average price per share. Common stock, shares issuable under agreement Common Stock Shares Issuable Under Agreement Common stock shares issuable under agreement. Amount due from customer Amount due from agreement Contract With Customer Asset Net Deferred revenue Initial lease term Lessee Operating Lease Term Of Contract Lease term description Lessee Operating Lease Description Area of rentable office and laboratory space Area Of Land Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] Letter of Credit Letter Of Credit [Member] Credit Facility Credit Facility [Domain] Credit Facility Credit Facility [Axis] Tenth year of lease term Tenth Year Of Lease Term [Member] Tenth year of lease term. Second twelve months of lease term Second Twelve Months Of Lease Term [Member] Second twelve months of lease term. First year of lease term First Year Of Lease Term [Member] Other assets Increase Decrease In Other Operating Assets Prepaid expenses and other current assets Increase Decrease In Prepaid Deferred Expense And Other Assets Accounts receivable Increase Decrease In Accounts Receivable Changes in operating assets and liabilities Increase Decrease In Operating Capital [Abstract] Stock-based compensation expense Share Based Compensation Accretion Amortization Of Discounts And Premiums Investments Amortization of intangible assets Amortization Of Intangible Assets Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Net loss Profit Loss Cash flows from operating activities: Net Cash Provided By Used In Operating Activities [Abstract] Statement Of Cash Flows [Abstract] Non-cash lease expense Noncash Lease Expense Noncash lease expense. Depreciation and amortization Depreciation And Amortization Excluding Amortization Of Intangible Assets Depreciation and amortization excluding amortization of intangible assets. Stock-based compensation Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value Issuance of common stock under the ESPP, shares Stock Issued During Period Shares Employee Stock Purchase Plans Issuance of common stock under the ESPP Less imputed interest Lessee Operating Lease Liability Undiscounted Excess Amount Total lease payments Lessee Operating Lease Liability Payments Due Lessee Operating Lease Liability Payments Due Year Three Lessee Operating Lease Liability Payments Due Year Two Lessee Operating Lease Liability Payments Due Next Twelve Months Weighted-average remaining lease term (in years) Weighted Average Remaining Lease Term [Abstract] Weighted average remaining lease term. Supplemental balance sheet information related to leases: Supplemental Balance Sheet Information Related To Leases [Abstract] Supplemental balance sheet information related to leases. Operating cash flows from operating leases Operating Lease Payments Cash paid for amounts included in the measurement of lease liabilities Cash Paid For Amounts Included In Measurement Of Lease Liabilities [Abstract] Cash paid for amounts included in measurement of lease liabilities. Rent expense Operating Lease Expense Letter of credit outstanding, amount Letters Of Credit Outstanding Amount Improvement allowance from recoverable rent Improvement Allowance From Recoverable Rent Improvement allowance from recoverable rent. Maximum one-time improvement allowance Maximum Improvement Allowance Maximum improvement allowance. Annual lease rent Operating Leases Rent Expense Annual Base Rent Operating leases rent expense annual base rent. Extended lease term Lessee Operating Lease Renewal Term Operating Lease Weighted Average Discount Rate Percent Operating lease Operating Lease Weighted Average Remaining Lease Term1 Present value of lease liabilities Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] Operating Lease Liability Current Statement Of Financial Position Extensible List Weighted-average discount rate Weighted Average Discount Rate [Abstract] Weighted average discount rate. Development, Regulatory and Commercial Milestone Payments Development Regulatory And Commercial Milestone Payments [Member] Development regulatory and commercial milestone payments. Contingent Consideration Type Contingent Consideration Type [Domain] Contingent Consideration by Type Contingent Consideration By Type [Axis] Discovery Agreement Discovery Agreement [Member] Discovery agreement. Seattle Genetics Agreement Seattle Genetics Agreement [Member] Seattle genetics agreement. CD71 Agreement C D71 Agreement [Member] CD 71 agreement. U.S UNITED STATES Geographical Segment Geographical [Domain] Geographical Statement Geographical [Axis] Maximum Maximum [Member] Minimum Minimum [Member] Statistical Measurement Range [Member] Statistical Measurement Range [Axis] Collaborative Arrangement Collaborative Arrangement [Member] Collaborative Arrangement and Arrangement Other than Collaborative Arrangements And Nonarrangement Transactions [Member] Collaborative Arrangement and Arrangement Other than Collaborative Type Of Arrangement [Axis] Number of collaboration agreements Number Of Collaboration Agreements Number of collaboration agreements. Percentage of net profits or net losses related to development and commercialization costs Percentage Of Net Income Or Net Losses Related To Development And Commercialization Costs Percentage of net Income or net losses related to development and commercialization costs. Revenue Revenues Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] Bristol Myers Squibb Bristol Myers Squibb Company Bristol Myers Squibb Company [Member] Fair Value By Fair Value Hierarchy Level [Axis] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Amortized Cost Total current liabilities Liabilities Current Deferred revenue, current portion Contract With Customer Liability Current Total Accrued liabilities Accrued Liabilities Current Accounts payable Accounts Payable Current Current liabilities: Liabilities Current [Abstract] Liabilities and Stockholders' Equity Liabilities And Stockholders Equity [Abstract] Total assets Assets Other assets Other Assets Noncurrent Operating lease right-of-use asset Operating Lease Right Of Use Asset Restricted Cash Noncurrent Goodwill Goodwill Intangible assets, net Indefinite Lived Intangible Assets Excluding Goodwill Property and equipment, net Property Plant And Equipment Net Total current assets Assets Current Prepaid expenses and other current assets Prepaid Expense And Other Assets Current Accounts receivable Accounts Receivable Net Current Short-term investments Available For Sale Securities Debt Securities Current Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Current assets: Assets Current [Abstract] Assets Assets [Abstract] Statement [Line Items] Statement [Line Items] Convertible Preferred Stock Convertible Preferred Stock [Member] Class of Stock Class Of Stock [Domain] Class of Stock Lessee Operating Lease Liability Payments Remainder Of Fiscal Year Maturity of operating lease liabilities Operating Lease Liabilities Payments Due [Abstract] Operating lease Balance at Beginning of Period Balance at End of Period Contract With Customer Liability Contingent milestone payments receivable Contingent Milestone Payments Receivable Future contingent milestone payment receivable. Milestone payments received Milestone Payment Received Milestone payment received. Number of targets selected Number Of Targets Selected Number of targets selected. Number of targets Number Of Targets Number of targets. Upfront payment received Proceeds From Collaborators Sublicense fees paid Payments Of Sublicense Fees Payments of sublicense fees. Milestone payment received Milestone Payments Received From Revenue Recognized During Period Milestone payments received from revenue recognized during period. Contingent payments receivable upon achieving development, regulatory and commercial milestones Contingent Payments Receivable Upon Achieving Development Regulatory And Commercial Milestones Contingent payments receivable upon achieving development, regulatory and commercial milestones. Profit split on U.S. sales Contingent Payments Receivable Profit Split On Sales Contingent payments receivable profit split on sales. Transferred over Time Transferred Over Time [Member] Timing of Transfer of Good or Service Timing Of Transfer Of Good Or Service [Domain] Timing of Transfer of Good or Service Timing Of Transfer Of Good Or Service [Axis] Second Target Second Target [Member] Second target. Product and Service Products And Services [Domain] Product and Service Product Or Service [Axis] Organization Consolidation And Presentation Of Financial Statements [Abstract] Research and Collaboration Agreements Research And Collaboration Agreements [Text Block] Research and collaboration agreements. Accrued Liabilities Accounts Payable And Accrued Liabilities Disclosure [Text Block] Accrued Liabilities Current [Abstract] Fair Value Disclosures [Text Block] Fair Value Disclosures [Abstract] Net Loss Per Share Earnings Per Share [Text Block] Earnings Per Share [Abstract] Basis of Presentation and Summary of Significant Accounting Policies Basis Of Presentation And Significant Accounting Policies [Text Block] Accounting Policies [Abstract] Description of the Business Nature Of Operations Disclosure Text Block [Abstract] Purchases of property and equipment in accounts payable and accrued liabilities Capital Expenditures Incurred But Not Yet Paid Supplemental disclosures of noncash investing items: Noncash Investing And Financing Items [Abstract] Total Cash, cash equivalents and restricted cash, beginning of period Cash, cash equivalents and restricted cash, end of period Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect Net cash provided by financing activities Net Cash Provided By Used In Financing Activities Proceeds from employee stock purchase plan and exercise of stock options Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options Proceeds from issuance of common stock, net of issuance costs Common stock, value of shares issued in connection with agreement Proceeds From Issuance Of Common Stock Cash flows from financing activities: Net Cash Provided By Used In Financing Activities [Abstract] Net Cash Provided By Used In Investing Activities Proceeds From Sale Of Available For Sale Securities Debt Purchases of property and equipment Payments To Acquire Property Plant And Equipment Cash flows from investing activities: Net Cash Provided By Used In Investing Activities [Abstract] Net Cash Provided By Used In Operating Activities Cash Cash Equivalents And Short Term Investments Amortized Cost Basis Anti-dilutive securities excluded from computation of diluted net loss per share Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Options and ESPP to purchase common stock Options And E S P P To Purchase Common Stock [Member] Options and ESPP to purchase common stock. 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Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Summary of significant accounting policies. Cash And Cash Equivalents [Abstract] Schedule of Maturity of Operating Lease Liabilities Lessee Operating Lease Liability Maturity Table [Text Block] Summary of Supplemental Information Related to Leases Supplemental Information Related To Leases Table [Text Block] Supplemental information related to leases. Total Stock-based Compensation Recognized Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block] Schedule of Activities Under Company's Stock Option Plans Schedule Of Share Based Compensation Stock Options Activity Table [Text Block] Summary of Contract Liabilities Contract With Customer Asset And Liability Table [Text Block] Schedule of Revenue by Collaboration Partners Disaggregation Of Revenue Table [Text Block] Schedule of Accrued Liabilities Schedule Of Accrued Liabilities Table [Text Block] Schedule Of Fair Value Assets And Liabilities Measured On Recurring Basis Table [Text Block] Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block] Schedule of Cash, Cash Equivalents, and Restricted Cash Schedule Of Cash Cash Equivalents And Restricted Cash Table [Text Block] Schedule of cash, cash equivalents, and restricted cash. Adopted Accounting Pronouncements New Accounting Pronouncements Policy Policy [Text Block] Leases Lessee Leases Policy [Text Block] Stock-based Compensation Share Based Compensation Option And Incentive Plans Policy Research and Development Expenses Research And Development Expense Policy Contract Balances Revenue From Contract With Customer Policy [Text Block] Revenue Recognition Revenue Recognition Policy [Text Block] Comprehensive Income Policy Policy [Text Block] Marketable Securities Policy Restricted Cash Cash And Cash Equivalents Restricted Cash And Cash Equivalents Policy Cash and Cash Equivalents Cash And Cash Equivalents Policy [Text Block] Use of Estimates Use Of Estimates Unaudited Interim Financial Information Unaudited Interim Financial Information Policy [Text Block] Unaudited interim financial information. Basis of Presentation Basis Of Accounting Policy Policy [Text Block] Income Tax Disclosure [Text Block] Income Tax Disclosure [Abstract] Commitments and Contingencies Commitments And Contingencies Disclosure [Text Block] Commitments And Contingencies Disclosure [Abstract] Leases Lessee Operating Leases [Text Block] Leases [Abstract] Stock-Based Compensation Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Equity [Abstract] Common Stock Common Stock [Text Block] Common stock. Research And Development [Abstract] License Agreements License Agreement Disclosure [Text Block] License agreement. Statement Class Of Stock [Axis] Statement [Table] Statement [Table] Statement Of Financial Position [Abstract] Property, Plant and Equipment, Net, Total Property, Plant and Equipment, Net, Beginning Balance Property, Plant and Equipment, Net, Ending Balance Share-based Payment Arrangement, Noncash Expense, Total Payments to Acquire Property, Plant, and Equipment, Total Common Stock, Shares, Outstanding, Beginning Balance Common Stock, Shares, Outstanding, Ending Balance Common Stock Shares Issued Common stock, shares authorized Common Stock Shares Authorized Common stock, par value Common Stock Par Or Stated Value Per Share Convertible Preferred stock, shares authorized Preferred Stock Shares Authorized Convertible Preferred stock, par value Preferred Stock Par Or Stated Value Per Share Total liabilities and stockholders' equity Liabilities And Stockholders Equity Total stockholders' equity Beginning balance Ending balance Stockholders Equity Accumulated deficit Retained Earnings Accumulated Deficit Accumulated Other Comprehensive Income Loss Net Of Tax Additional paid-in capital Additional Paid In Capital Common Stock Value Preferred Stock Value Stockholders' equity: Stockholders Equity [Abstract] Commitments and contingencies (Note 11) Commitments And Contingencies Total liabilities Liabilities Operating Lease Liability Noncurrent Deferred revenue, net of current portion Contract With Customer Liability Noncurrent Bristol-Myers Squibb Company. Astellas Pharma Inc. Astellas Astellas Pharma Inc [Member] Astellas Pharma Inc. Amgen Inc Amgen Amgen Inc [Member] Amgen Inc. AbbVie AbbVie Ireland Unlimited Company Abb Vie Ireland Unlimited Company [Member] AbbVie Ireland Unlimited Company. Counterparty Name Repurchase Agreement Counterparty Name [Domain] Counterparty Name Counterparty Name [Axis] Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table] Schedule Of Collaborative Arrangements And Noncollaborative Arrangement Transactions [Table] Other accrued expenses Other Accrued Liabilities Current Current operating lease liabilities Operating lease liabilities - short term Operating Lease Liability Current Legal and professional expenses Accrued Professional Fees Current Payroll and related expenses Employee Related Liabilities Current Research and clinical expenses Accrued Research And Clinical Current Accrued research and clinical current. Available For Sale Securities Debt Securities Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax Debt Securities Available For Sale Allowance For Credit Loss Short-term Investments, Amortized Cost Available For Sale Debt Securities Amortized Cost Basis Restricted cash Restricted Cash And Cash Equivalents At Carrying Value 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] Level I Fair Value Inputs Level1 [Member] Fair Value Hierarchy and NAV Fair Value Measurements Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV Contract with Customer, Asset, after Allowance for Credit Loss, Total Revenues, Total Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised, Total Increase (Decrease) in Prepaid Expense and Other Assets, Total Debt Securities, Available-for-sale, Current, Total Increase (Decrease) in Other Operating Assets, Total General and Administrative Expense, Total Contract with Customer, Liability, Total Common Stock, Value, Issued, Total Common Stock, Value, Issued, Beginning Balance Common Stock, Value, Issued, Ending Balance Goodwill, Total Goodwill, Beginning Balance Goodwill, Ending Balance Accumulated Other Comprehensive Income (Loss), Net of Tax, Total Revenue from Contract with Customer, Excluding Assessed Tax, Total APIC, Share-based Payment Arrangement, Increase for Cost Recognition, Total Preferred Stock, Value, Issued, Total Preferred Stock, Value, Issued, Beginning Balance Preferred Stock, Value, Issued, Ending Balance Amortization of Intangible Assets, Total Accounts Receivable, after Allowance for Credit Loss, Current, Total Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total Retained Earnings (Accumulated Deficit), Total Retained Earnings (Accumulated Deficit), Beginning Balance Retained Earnings (Accumulated Deficit), Ending Balance Debt Securities, Available-for-sale, Allowance for Credit Loss, Total Debt Securities, Available-for-sale, Allowance for Credit Loss, Beginning Balance Debt Securities, Available-for-sale, Allowance for Credit Loss, Ending Balance Restricted Cash and Cash Equivalents, Current, Total Cash and Cash Equivalents, at Carrying Value, Total Cash and Cash Equivalents, at Carrying Value, Beginning Balance Cash and Cash Equivalents, at Carrying Value, Ending Balance Gross Unrealized Holding Losses Cash Cash Equivalents And Short Term Investments Accumulated Gross Unrealized Loss Before Tax Gross Unrealized Holding Gains Cash Cash Equivalents And Short Term Investments Accumulated Gross Unrealized Gain Before Tax Allowance for Credit Losses Cash Cash Equivalents And Short Term Investments Allowance For Credit Loss Common Stock, Shares, Issued, Total OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax, Total Other Assets, Noncurrent, Total Additional Paid in Capital, Total Additional Paid in Capital, Beginning Balance Additional Paid in Capital, Ending Balance Increase (Decrease) in Accounts Payable, Total Accounts Payable, Current, Total Employee-related Liabilities, Current, Total Other Nonoperating Income (Expense), Total Debt Securities, Available-for-sale, Total Income Tax Expense (Benefit), Total Research and Development Expense, Total Indefinite-lived Intangible Assets (Excluding Goodwill), Total Indefinite-lived Intangible Assets (Excluding Goodwill), Beginning Balance Indefinite-lived Intangible Assets (Excluding Goodwill), Ending Balance Restricted cash - non-current assets Restricted cash Issuance of common stock in follow-on offering, net of issuance costs, shares Accrued Liabilities Accrued Liabilities Milestone payment received Operating lease liabilities - long term Non-current operating lease liabilities Total operating lease liabilities Total operating lease liabilities Payments to Acquire Investments Payments to Acquire Investments, Total Long-term Investments Long-term Investments, Total Fair Value Measurements and Investments Schedule of Investments Subject to Fair Value Measurements on a Recurring Basis 2021 2022 2023 2024 Lessee operating lease liability payments due year four and thereafter Lessee Operating Lease Liability Payments Due Year Four And Thereafter 2025 and beyond Cash, cash equivalents and investments, amortized cost basis. Cash, cash equivalents and investments, allowance for credit loss. Cash, cash equivalents and investments, accumulated gross unrealized gain before tax. Cash, cash equivalents and investments, accumulated gross unrealized loss before tax. Cash Cash Equivalents And Investments Cash Cash Equivalents And Investments Aggregate Fair Value Investments, Allowance for Credit Losses Investments, Amortized Cost Investments, Gross Unrealized Holding Gains Investments, Gross Unrealized Holding Losses Investments, Aggregate Fair Value Debt securities, available for sale, maturity period. 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