Securities Related Claims Securities Related Claims [Member] Securities related claims. Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Document Type Document Type ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Aggregate Intrinsic Value, outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Interest income and other income (expense), net Other Nonoperating Income (Expense) Number of shares, options granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Weighted Average Grant Date Fair Value, Vested and released (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Mission Bay Lease Mission Bay Lease [Member] Mission bay lease. Number of additional shares available for award grants Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Nektar Nektar [Member] Nektar [Member] Leases Lessee, Leases [Policy Text Block] Accrued contract manufacturing expenses Accrued Contract Manufacturing Expense Current Accrued contract manufacturing expense current. Range [Domain] Statistical Measurement [Domain] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Security Exchange Name Security Exchange Name Amgen, Inc. Amgen, Inc. Amgen Inc [Member] Amgen Inc. Income (loss) from operations Operating loss Operating Income (Loss) Total current liabilities Liabilities, Current Changes in Deferred Revenue Balance from Collaboration Agreements Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Additional indication payment Collaborative Arrangement, Additional Indication Payment Collaborative Arrangement, Additional Indication Payment Weighted Average Grant Date Fair Value, Beginning balance (in dollars per share) Weighted Average Grant Date Fair Value, Ending balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Opdivo Opdivo [Member] Opdivo. Commitments and contingencies Commitments and Contingencies Maximum 401(k) per employee, percentage of annual salary Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent Long-term investments Debt Securities, Available-for-sale, Noncurrent ASSETS Assets [Abstract] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] 2026 and thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Revenue, Major Customer [Line Items] Revenue, Major Customer [Line Items] UCB U C B Pharma [Member] UCB Pharma. Employee Stock Purchase Plan Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan Furniture, fixtures, and other Furniture and Fixtures [Member] Shares issued under equity compensation plans Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Entity Address, State or Province Entity Address, State or Province Vested and released (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Income tax expense (benefit) at federal statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Operating lease, payments Operating Lease, Payments Accounts payable Accounts Payable, Current Shipping and Handling Costs Contract With Customer Shipping And Handling Costs Policy [Policy Text Block] Contract with customer shipping and handling costs. License, collaboration and other revenue License Collaboration And Other Revenue [Member] License collaboration and other revenue. Accumulated deficit Retained Earnings (Accumulated Deficit) Operating lease right-of-use assets Operating Lease, Right-of-Use Asset Eligible additional cash payments receivable upon achievement of certain sales milestones Eligible Additional Cash Payments Receivable Upon Achievement Of Certain Sales Milestones Eligible additional cash payments receivable upon achievement of certain sales milestones. Cash And Investments In Marketable Securities [Table] Cash And Investments In Marketable Securities [Table] Cash and Investments in Marketable Securities [Table] 2021 Lessee, Operating Lease, Liability, to be Paid, Year One Number of shares, outstanding, beginning balance (in shares) Number of shares, outstanding, ending balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Percentage of sharing in Phase 2 development costs Percentage Of Sharing In Phase Two Development Costs Percentage of sharing in Phase 2 development costs. 2024 Lessee, Operating Lease, Liability, to be Paid, Year Four Total unrecognized compensation costs Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Customer Customer [Axis] State Current State and Local Tax Expense (Benefit) Beginning Balance (in shares) Ending Balance (in shares) Shares, Outstanding Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares designated, issued or outstanding at December 31, 2020 or 2019 Preferred Stock, Value, Issued Contract with customer, asset, reclassified to receivable Contract with Customer, Asset, Reclassified to Receivable Partner One Partner One [Member] Partner One Income Taxes Income Tax, Policy [Policy Text Block] Total lease costs Lease, Cost Estimate for royalties resulting from net sales Contract with Customer, Estimate for Royalties Resulting from Net Sales Contract with Customer, Estimate for Royalties Resulting from Net Sales Buildings Building [Member] Number of shares, exercisable (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Common stock, par value (in usd per share) Common Stock, Par or Stated Value Per Share Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Other long-term liabilities Other Liabilities, Noncurrent Percentage of sharing production costs Percentage Of Sharing In Production Costs Percentage of sharing in production costs. Less: unamortized transaction costs Liabilities On Sale Of Future Royalties Unamortized Transaction Costs Liabilities on sale of future royalties, unamortized transaction costs. BMS Collaboration Agreement B M S Collaboration Agreement [Member] BMS collaboration agreement. Income Taxes Disclosure [Table] Income Taxes Disclosure [Table] Income taxes disclosure. Work-in-process Inventory, Work in Process, Net of Reserves Other Other Partner [Member] Other. Stock-based compensation APIC, Share-based Payment Arrangement, Increase for Cost Recognition Effect of exchange rates on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Construction-in-progress Construction in Progress, Gross Non-cash royalty revenue related to sale of future royalties Non-cash royalty revenue Non Cash Royalty Revenue Related To Sale Of Future Royalties Non cash royalty revenue related to sale future royalties. Inventory Total inventory Inventory, Net Total revenue Revenue recognized from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Percentage revenue from customers Concentration Risk, Percentage 7.75% Senior Secured Notes Due October 2020 Seven Point Seven Five Percent Senior Secured Notes Due October Two Thousand And Twenty [Member] Seven point seven five percent senior secured notes due October two thousand and twenty. Geographical Geographical [Domain] Stock options term under equity incentive plans Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Secured Notes [Table] Secured Notes [Table] Secured notes. Statement [Line Items] Statement [Line Items] Foreign Deferred Foreign Income Tax Expense (Benefit) Federal orphan drug credits Federal Orphan Drug Credits Federal orphan drug credits. Schedule of Collaborative Arrangements and Non-collaborative Arrangement Transactions [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Entity Voluntary Filers Entity Voluntary Filers Amount of net sales to fund external costs incurred cap Amount of Net Sales to Fund External Costs Incurred Cap Amount of Net Sales to Fund External Costs Incurred Cap Statement [Table] Statement [Table] Premium on equity issuance Income Tax Reconciliation Premium On Equity Issuance Income tax reconciliation premium on equity issuance. Cash and Investments in Marketable Securities [Line Items] Cash And Investments In Marketable Securities [Line Items] Cash and Investments in Marketable Securities [Line Items] Leased space delivered (in sq ft) Area Of Leased Space Delivered Area of leased space delivered. Range Statistical Measurement [Axis] Upfront Payment Arrangement Up-front Payment Arrangement [Member] Bristol Myers Squibb Collaboration Agreement Bristol Myers Squibb Collaboration Agreement [Member] Bristol Myers Squibb collaboration agreement. Partner Three Partner Three [Member] Partner Three Non-cash interest expense on liability related to sale of future royalties Non-cash interest expense on liability related to sale of future royalties Non-cash interest expense Non Cash Interest Expense Related To Sale Of Royalties Non-cash interest expense related to sale of royalties. Potential future additional payments for development milestones Potential Development Milestones Potential development milestones. Research and Development Arrangement, Contract to Perform for Others, Type Research and Development Arrangement, Contract to Perform for Others, Type [Axis] Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Net expense reimbursements from collaboration partner Net Expense Reimbursements From Collaboration Partner Net expense reimbursements from collaboration partner. Percentage of net sales to fund external costs incurred, due to reduction of 2 percentage points Percentage Of Net Sales To Fund External Costs Incurred, Due To Reduction Of 2 Percentage Points Percentage Of Net Sales To Fund External Costs Incurred, Due To Reduction Of 2 Percentage Points Research and Development Arrangement, Contract to Perform for Others, Type Research and Development Arrangement, Contract to Perform for Others, Type [Domain] Obligations of U.S. government agencies US Government Agencies Debt Securities [Member] Phase 1 Clinical Development Phase One Clinical Development [Member] Phase 1 clinical development. India INDIA Stock-based compensation Income Tax Reconciliation Expense Share Based Compensation Cost Income tax reconciliation expense share based compensation cost. Liabilities related to the sales of future royalties, net Liability related to the sale of future royalties, net Liability Related To Sale Of Potential Future Royalties Non Current Net Of Issuance Costs Liability related to sale of potential future royalties non current net of issuance costs. Upfront and milestone payments received from license agreements Upfront And Milestone Payments Received From License Agreements Upfront and milestone payments received from license agreements. Entity Small Business Entity Small Business Non-cash interest expense on liability related to sale of future royalties Income Tax Reconciliation Non Deductible Expense For Liability Related Sale Of Future Royalties Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other nondeductible expenses. Potential future development, regulatory and sales milestones Potential Development Regulatory And Sales Milestones Potential development regulatory and sales milestones. Basis of Presentation, Principles of Consolidation and Use of Estimates Consolidation, Policy [Policy Text Block] Percentage of sharing development costs Percentage Of Sharing In Development Costs Percentage of sharing in development costs. Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] License And Collaboration Agreements [Table] License And Collaboration Agreements [Table] License and collaboration agreements. Number of operating business segment Number Of Operating Business Segment Number of operating business segment. Fair Value Hierarchy and NAV Fair Value Hierarchy and NAV [Domain] Weighted-Average Remaining Contractual Life, exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Received under right to sublicense agreement Payments Received Under Rights To Sublicense Agreement Payments received under rights to sublicense agreement. Number of reporting unit evaluated for goodwill Number Of Reporting Units To Evaluate Goodwill For Impairment Number of reporting units to evaluate goodwill for impairment Amendment Flag Amendment Flag Revenue by geographic area Geographic Areas, Revenues from External Customers [Abstract] Payments to RPI Partial Repayment Of Royalty Sale Proceeds Partial repayment of royalty sale proceeds. Black-Scholes Option-Pricing Model Assumptions Used to Calculate Fair Value of Employee Stock Options Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Weighted average shares outstanding used in computing net income (loss) per share Weighted Average Number of Shares Outstanding, Diluted [Abstract] Liabilities Related to the Sales of Future Royalties Liability Related To Sale Of Potential Future Royalties [Text Block] Liability related to sale of potential future royalties. Write off of prepayment Write Off Of Prepayment Write Off Of Prepayment Organization Organization [Policy Text Block] Organization. Research and Development Expense Research and Development Expense, Policy [Policy Text Block] Purchase and Sale Agreement with RPI Purchase And Sale Agreement [Member] Purchase and sale agreement. Laboratory equipment Laboratory Equipment [Member] Laboratory equipment. Portfolio of Cash and Investments in Marketable Securities Fair Value, Assets Measured on Recurring Basis [Table Text Block] Impairment of assets and other costs for terminated program Impairment Of Assets And Other Costs For Terminated Program Impairment of equipment and other costs for terminated program. Number of common stock shares available for stock options grants Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Other accrued expenses Other Accrued Liabilities, Current Purchase commitments related to contract manufacturing, clinical development and certain other items Purchase Commitment, Remaining Minimum Amount Committed Astra Zeneca Ab Astra Zeneca Ab [Member] AstraZeneca AB. Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Entity Central Index Key Entity Central Index Key Short-term investments Debt Securities, Available-for-sale, Current Development costs exceeded Development Costs Exceeded Development Costs Exceeded Received upfront and milestone payment Upfront And Milestone Payments Received Under License Agreement Upfront and milestone payments received under license agreement. Senior Notes Senior Notes [Member] Contract with Customer, Sales Channel [Domain] Contract with Customer, Sales Channel [Domain] Accrued clinical trial expenses Accrued Clinical Trial Expenses Current Accrued clinical trial expenses current. Geographical Geographical [Axis] Subsequent Event Subsequent Events [Text Block] Change in valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Liability Related To Sale Of Potential Future Royalties [Abstract] Liability Related To Sale Of Potential Future Royalties [Abstract] Liability related to sale of potential future royalties. Amortized Cost Debt Securities, Available-for-sale, Amortized Cost AstraZeneca-Kirin Astra Zeneca Agreement With Kirin [Member] AstraZeneca agreement with Kirin. Remaining amount allocated to transaction price Remaining Amount Allocated To Transaction Price Remaining amount allocated to transaction price. Gross unrealized gains Gross Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Property, Plant and Equipment, Type Long-Lived Tangible Asset [Axis] Employee Stock Purchase Plan Employee Stock [Member] Total assets Liabilities And Stockholders Equity Deficit [Abstract] Liabilities and stock holders equity (deficit) abstract.. Income Statement Location Income Statement Location [Axis] Entity Common Stock, Shares Outstanding (in shares) Entity Common Stock, Shares Outstanding Income Statement Location Income Statement Location [Domain] Income tax research credits Research credits Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount Obligations under Director and Officer Indemnifications per incident Obligations Under Director And Officer Indemnifications Per Incident Obligations under director and officer indemnifications per incident. Percentage of net sales to fund external costs incurred Percentage of Net Sales to Fund External Costs Incurred Percentage of Net Sales to Fund External Costs Incurred 2022 Lessee, Operating Lease, Liability, to be Paid, Year Two State State and Local Jurisdiction [Member] Hemophilia, Including ADYNOVATE and ADYNOVITM Hemophilia Including A D Y N O V A T E And A D Y N O V I [Member] Hemophilia including ADYNOVATE and ADYNOVI. Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Computer equipment and software Computer Furniture And Other [Member] Furniture computer and other. Federal Current Federal Tax Expense (Benefit) Revenue by Geographic Area Schedule of Revenue from External Customers Attributed to Foreign Countries by Geographic Area [Table Text Block] Lease, Cost Lease, Cost [Table Text Block] Non-cash royalty revenue related to sale of future royalties Incometax Reconciliation Income Tax Sale Of Future Royalties Income tax reconciliation income tax sale of future royalties. 2023 Lessee, Operating Lease, Liability, to be Paid, Year Three Other assets Other Assets, Noncurrent Company share of development costs, annual cap Company Share Of Development Costs, Annual Cap Company Share Of Development Costs, Annual Cap Deferred Revenue Arrangement Type Deferred Revenue Arrangement Type [Axis] Plan Name Plan Name [Axis] Segment Reporting Segment Reporting Disclosure [Text Block] Issuance of common stock to Bristol-Myers Squibb (Note 10) Proceeds From Issuance Of Common Stock Net Of Issuance Costs Proceeds From Issuance Of Common Stock Net Of Issuance Costs Sale of stock to Bristol-Myers Squibb (Note 10) Stock Issued During Period, Value, New Issues Other assets Assets Schedule Of Leases [Table] Schedule Of Leases [Table] Schedule Of Leases [Table] Units Issued, Beginning balance (in shares) Units Issued, Ending balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Sale of future royalties transaction costs Sale of Future Royalties Transaction Costs Sale of Future Royalties Transaction Costs Title of 12(b) Security Title of 12(b) Security Maximum total additional cash payments receivable upon achievement of certain development and regulatory milestones Collaborative Arrangements Maximum Aggregate Additional Cash Payments Receivable Upon Achievement Of Development And Regulatory Milestones Collaborative arrangements maximum aggregate additional cash payments receivable upon achievement of development and regulatory milestones. Legal Matters Legal Matters [Member] Legal Matters Net operating loss carryforward for income tax Net Operating Loss Carryforward For Income Tax Net operating loss carryforward for income tax. Weighted-average grant-date fair value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Subsequent Event Type [Axis] Subsequent Event Type [Axis] Hemophilia Hemophilia [Member] Hemophilia. Antidilutive Securities Antidilutive Securities [Axis] Cost of goods sold Cost of Sales [Member] Interest expense Interest Expense 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] Percentage of upfront payment, market access milestones, royalties and sales milestones Percentage Of Upfront Payment Market Access Milestone Payments Royalties And Sales Milestone Payments Percentage of upfront payment, market access milestone payments, royalties and sales milestone payments. Depreciation and amortization expenses Depreciation, Depletion and Amortization Provision for Income Taxes Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Amount of transaction price allocated to performance obligation Amount Of Transaction Price Allocated To Performance Obligation Amount of transaction price allocated to performance obligation. Product and Service Product and Service [Axis] Total liabilities Liabilities Investment Type Investment Type [Axis] Percentage of purchase price of stock Percentage Of Purchase Price Of Stock Percentage of purchase price of stock. Stock Options and Restricted Stock Units Stock Options And Restricted Stock Units [Member] Stock options and restricted stock units. Recognized over a weighted-average period Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Non-US Non-US [Member] Less: portion representing interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Summary of Liability Related to Potential Future Royalties Schedule Of Liability Related To Sale Of Potential Future Royalties [Table Text Block] Schedule Of Liability Related To Sale Of Potential Future Royalties Development milestones received Recognition of previously unearned revenue Contract with Customer, Liability, Revenue Recognized Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Proceeds from shares issued under equity compensation plans Proceeds, Issuance of Shares, Share-based Payment Arrangement, Excluding Option Exercised Fair Value Hierarchy Level 1 Fair Value, Inputs, Level 1 [Member] Inventory and Significant Supplier Concentrations Inventory And Significant Supplier Concentrations [Policy Text Block] Inventory and significant supplier concentrations. Inventory Increase (Decrease) in Inventories Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Payment of transaction related to purchase and sale agreement if threshold is not achieved Payment of Transaction Related to Purchase and Sale Agreement if Threshold is not Achieved Payment of Transaction Related to Purchase and Sale Agreement if Threshold is not Achieved Accounts payable Increase (Decrease) in Accounts Payable Raw materials Inventory, Raw Materials, Net of Reserves SFJ Pharmaceuticals SFJ Pharmaceuticals [Member] SFJ Pharmaceuticals Valuation allowance, increase (decrease) amount Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Liability Related To Sale Of Future Royalties [Table] Liability Related To Sale Of Future Royalties [Table] Liability related to sale of future royalties. Building and leasehold improvements Building And Leasehold Improvements [Member] Building and Leasehold Improvements. Debt Instrument Debt Instrument [Axis] Capital in Excess of Par Value Additional Paid-in Capital [Member] Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Antidilutive Securities, Name Antidilutive Securities, Name [Domain] Quarterly Financial Data Quarterly Financial Information [Table Text Block] Class of Stock [Line Items] Class of Stock [Line Items] Shares issued (in shares) Shares, Issued Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Estimated fair value of shares Estimated Fair Value Of Shares Estimated fair value of shares. Liability Related to the Sale of Future Royalties [Line Items] Liability Related To Sale Of Future Royalties [Line Items] Liability related to sale of future royalties. 2017 Performance Incentive Plan Two Thousand Seventeen Performance Incentive Plan [Member] Two thousand seventeen performance incentive plan. Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Liability Related To The Sale Of Future Royalties [Roll Forward] Liability Related To The Sale Of Future Royalties [Roll Forward] Liability Related To The Sale Of Future Royalties [Roll Forward] Variable lease cost Variable Lease, Cost Operating lease liabilities Deferred Tax Assets, Lease Liability Deferred Tax Assets, Lease Liability Income (loss) before provision for income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Loss Contingency Nature Loss Contingency Nature [Axis] Impairment of Assets and Other Costs for Terminated Program Impairment of Assets and Other Costs for Terminated Program [Policy Text Block] Impairment of Assets and Other Costs for Terminated Program Research and development Research and development expenses Research and Development Expense NKTR-358 Nektar Three Five Eight [Member] Nektar three five eight. Principal and interest repaid on senior notes Repayments Of Long Term Debt, Including Interest Repayments Of Long Term Debt, Including Interest Subsequent Event Subsequent Event [Member] Property, Plant and Equipment Property, Plant and Equipment [Member] Commercial Agreements Commercial Agreements [Member] Commercial Agreements Weighted-Average Exercise Price per Share, outstanding, beginning balance (in dollars per share) Weighted-Average Exercise Price per Share, outstanding, ending balance (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Comprehensive Income (Loss) Comprehensive Income, Policy [Policy Text Block] Federal Domestic Tax Authority [Member] Reclassifications Reclassification, Comparability Adjustment [Policy Text Block] Royalty revenue Royalty [Member] Percentage of regulatory milestones payments will be reduced if conditions occur Percentage Of Development Milestones Payments To Be Received If Conditions Occur Percentage of development milestones payments, to be received, if conditions occur. Letter of credit Letters of Credit Outstanding, Amount Common stock, shares authorized (in shares) Common Stock, Shares Authorized Restricted Stock Unit Award Activity Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Concentration Risk Type Concentration Risk Type [Axis] Weighted-average of potentially dilutive securities (stock options and RSUs) included in calculation of diluted securities under treasury stock method (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Federal Deferred Federal Income Tax Expense (Benefit) 7.75 Percent Senior Secured Notes Due October 2020 7.75 Percent Senior Secured Notes Due October 2020 [Member] 7.75 percent senior secured notes due October 2020 Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Accrued compensation Increase (Decrease) in Employee Related Liabilities Income Statement [Abstract] Income Statement [Abstract] Accumulated Other Comprehensive Income/(Loss) AOCI Attributable to Parent [Member] Service period for stock-based compensation award granted Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period Repayment of senior notes Principal amount repaid Repayments of Senior Debt Number of shares available for issuance under equity compensation plans Number Of Securities Available For Issuance Under Equity Compensation Plans Number of securities remaining available for issuance under equity compensation plans. Operating lease liability, less current portion Operating lease liabilities, less current portion Operating Lease, Liability, Noncurrent Interest Receivable Interest Receivable Cash and Investments in Marketable Securities, Including Cash Equivalents Cash, Cash Equivalents and Investments [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Reimbursement of expenses Reimbursement Of Expenses Reimbursement of expenses. Current assets: Assets, Current [Abstract] Income Tax Authority Income Tax Authority [Domain] License And Collaboration Agreements [Line Items] License And Collaboration Agreements [Line Items] License and collaboration agreements. Investments in marketable securities Investments, Fair Value Disclosure Consolidated Entities Consolidated Entities [Axis] Comprehensive income (loss) Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent License, collaboration and other revenue License Collaboration Other Revenue Revenue earned during the period relating to consideration received from another party for the right to use, but not own, certain of the entity's intangible assets. Revenue may contain one or more of the following elements: upfront fees, contract research, milestone payments, manufacturing and supply, royalties, and license fees. Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Preferred stock, par value (in usd per share) Preferred Stock, Par or Stated Value Per Share Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Income Tax Provision Related to Continuing Operations Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Counterparty Name Counterparty Name [Domain] Legal Entity Legal Entity [Axis] Purchases of property, plant and equipment Payments to Acquire Property, Plant, and Equipment City Area Code City Area Code Consolidation Items Consolidation Items [Domain] Income Tax Authority Income Tax Authority [Axis] Document Period End Date Document Period End Date Senior Secured Notes Long-term Debt [Text Block] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Accounts Receivable and Significant Customer Concentrations Accounts Receivable And Significant Customer Concentrations [Policy Text Block] Accounts receivable and significant customer concentrations. Litigation matters, liabilities Loss Contingency Accrual Common stock, shares reserved for issuance in equity compensation plans Common Stock, Capital Shares Reserved for Future Issuance Director Director [Member] Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Success-based payments, first indication, period to be paid Collaborative Arrangement, Success-based Payments, First Indication, Period to be Paid Collaborative Arrangement, Success-based Payments, First Indication, Period to be Paid Quarterly Financial Information Disclosure [Abstract] Quarterly Financial Information Disclosure [Abstract] Inventory Schedule of Inventory, Current [Table Text Block] Long-term Debt, Type Long-term Debt, Type [Domain] Liability related to the sale of future royalties Deferred Tax Assets, Liability Related to the Sale of Future Royalties Deferred Tax Assets, Liability Related to the Sale of Future Royalties Entity Entity [Domain] Success-based payments, second indication, period to be paid Collaborative Arrangement, Success-based Payments, Second Indication, Period to be Paid Collaborative Arrangement, Success-based Payments, Second Indication, Period to be Paid Selected Quarterly Financial Data Quarterly Financial Information [Text Block] Reductions Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions Schedule of Income before Income Tax, Domestic and Foreign Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] Property and equipment estimated useful lives Property, Plant and Equipment, Useful Life Contract with Customer, Sales Channel [Axis] Contract with Customer, Sales Channel [Axis] Deferred revenue Increase (Decrease) in Contract with Customer, Liability Leases Lessee, Operating Leases [Text Block] Amended and Restated 2017 Plan Amended and Restated 2017 Plan [Member] Amended and Restated 2017 Plan Net deferred tax assets Deferred Tax Assets, Net Concentration Risk Benchmark Concentration Risk Benchmark [Axis] Cost of goods sold Cost of goods sold Cost of Goods and Services Sold Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Fair Value Debt Securities, Available-for-sale Total operating costs and expenses Costs and Expenses Equity Components Equity Components [Axis] Finished goods Inventory, Finished Goods, Net of Reserves Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Share-based Payment Arrangement [Abstract] Debt Instrument, Name Debt Instrument, Name [Domain] Deferred tax assets before valuation allowance Deferred Tax Assets, Gross Minimum Minimum [Member] Consolidated Entities Consolidated Entities [Domain] Transaction costs related to sale of potential future royalties Transaction Costs Related To Sale Of Potential Future Royalties Transaction costs related to sale of potential future royalties. Operating lease liability, current portion Less: current portion Operating Lease, Liability, Current Potential future additional development and regulatory milestones Potential Development And Regulatory Milestones Potential development and regulatory milestones. Global commercialization profits and losses sharing percentage Profits And Losses Sharing Percentage Profits and losses sharing percentage. Total consideration received under agreements Aggregate Consideration Received From Agreements Aggregate consideration received from agreements. Milestone [Domain] Milestone [Domain] [Domain] for Milestone [Axis] Lease extension term Lease Extension Term Lease extension term. Weighted Average Grant Date Fair Value, Forfeited and canceled (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Entity Interactive Data Current Entity Interactive Data Current United States UNITED STATES Weighted-Average Exercise Price per Share, options exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Revenue: Revenues [Abstract] Cash and Investments in Marketable Securities 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] Deferred tax assets: Components of Deferred Tax Assets and Liabilities [Abstract] Stock Option Activity Under Equity Incentive Plans Share-based Payment Arrangement, Option, Activity [Table Text Block] Accounts Receivable Accounts Receivable [Member] Eli Lilly and Company Eli Lilly And Company [Member] Eli Lilly and Company. RSUs and PSUs RSUs and PSUs [Member] RSUs and PSUs Maturities of investments Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale Stock-Based Compensation Share-based Payment Arrangement [Policy Text Block] Non-Securities Related Claims Non Securities Related Claims [Member] Non-securities related claims. Customer Customer [Domain] Foreign Current Foreign Tax Expense (Benefit) Cumulative Effect, Period of Adoption, Adjustment Cumulative Effect, Period of Adoption, Adjustment [Member] Capital in excess of par value Additional Paid in Capital, Common Stock Secured Notes [Line Items] Secured Notes [Line Items] Secured notes. Entity Registrant Name Entity Registrant Name Subsequent Event Type [Domain] Subsequent Event Type [Domain] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Weighted average discount rate, percent Operating Lease, Weighted Average Discount Rate, Percent Less: lease incentives Lessee Operating Lease Liability Tenant Improvement Reimbursements Lessee operating lease liability tenant improvement reimbursements. Sales of property and plant Proceeds from Sale of Property, Plant, and Equipment Issuance costs Debt Issuance Costs, Net Cash and investments in marketable securities Total cash and investments in marketable securities Cash Restricted Cash Cash Equivalents And Available For Sale Investments Cash, restricted cash, cash equivalents, and available for sale investments. Change in control severance payment period for senior vice presidents and vice presidents Change In Control Severance Payment Period For Senior Vice Presidents and Vice Presidents Change In Control Severance Payment Period For Senior Vice Presidents and Vice Presidents Clinical Trial Agreement Clinical Trial Agreement [Member] Clinical trial agreement. Depreciable property, plant and equipment, net Depreciable Property Plant And Equipment Net Depreciable Property, plant and equipment, Net. Matching 401(k) employer contribution, maximum amount Deferred Compensation Arrangement with Individual, Contributions by Employer Consolidation Items Consolidation Items [Axis] Research and development Research and development Research and Development Expense [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Success-based payments, first indication Collaborative Arrangement, Success-based Payments, First Indication Collaborative Arrangement, Success-based Payments, First Indication Accounts receivable Accounts Receivable, after Allowance for Credit Loss, Current Royalty agreement contingent payment description Royalty Agreement Contingent Payment Description Royalty agreement contingent payment description. Total lease payments Lessee, Operating Lease, Liability, to be Paid Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Deferred tax liabilities: Components of Deferred Tax Liabilities [Abstract] Annual Sales Level Milestone Annual Sales Level Milestone [Member] Annual sales level milestone. Gross unrealized losses Gross Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Sale of Stock Sale of Stock [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Total deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Cash Cash Goodwill Goodwill Number of consecutive terms to extend lease Number Of Consecutive Terms To Extend Lease Number of consecutive five year terms to extend lease. Document Transition Report Document Transition Report Title of Individual [Axis] Title of Individual [Axis] Deferred: Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Arrangements and Non-arrangement Transactions Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Terminated Partnership Terminated Partnership [Member] Terminated Partnership [Member] Non-operating income (expense): Nonoperating Income (Expense) [Abstract] Percentage of regulatory milestones payments will be reduced under certain conditions Percentage Of Development Milestones Payments To Be Received Under Certain Conditions Percentage of development milestones payments, to be received under certain conditions. Fair Value Hierarchy Level 2 Fair Value, Inputs, Level 2 [Member] Schedule of Operating Lease Information Lessee, Operating Lease, Disclosure [Table Text Block] Other current assets Other Assets, Current Stock issued during period subject to lock-up and stand-still provisions period Stock Issued During Period Subject To Lock Up And Stand Still Provisions Period Stock issued during period subject to lock-up and stand-still provisions period. Current: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Number of shares, options forfeited and canceled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period General and administrative General and Administrative Expense [Member] Equity [Abstract] Equity [Abstract] Debt discount on transaction and facility fees Debt Discount On Transaction And Facility Fees Paid Debt discount on transaction and facility fees paid. Long term investment maturity period Long Term Investment Maturity Period Long term investment maturity period. Deferred revenue, current portion Contract with Customer, Liability, Current Subsequent Event [Line Items] Subsequent Event [Line Items] Change in control severance payment period for Chief Executive Officer Change In Control Severance Payment Period For Chief Executive Officer Change In Control Severance Payment Period For Chief Executive Officer Weighted-Average Exercise Price per Share, options granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Cumulative Effect, Period of Adoption [Axis] Cumulative Effect, Period of Adoption [Axis] Customer Concentration Risk Customer Concentration Risk [Member] Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Basic ( in dollars per share) Earnings Per Share, Basic Committed funding Collaborative Arrangement, Committed Funding Collaborative Arrangement, Committed Funding Organization And Summary Of Significant Accounting Policies [Line Items] Organization And Summary Of Significant Accounting Policies [Line Items] Organization and summary of significant accounting policies. Average weighted average expected life Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Entity File Number Entity File Number Forfeited and canceled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Debt Disclosure [Abstract] Debt Disclosure [Abstract] Weighted average remaining lease term Operating Lease, Weighted Average Remaining Lease Term Indemnification Obligation Indemnification Agreement [Member] Unrecognized Tax Benefits Schedule of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns Roll Forward [Table Text Block] Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Deferred Revenue Deferred Revenue [Domain] Stock-based compensation Total stock-based compensation Share-based Payment Arrangement, Expense Beginning balance Ending balance Unrecognized Tax Benefits Merger and Acquisition Related Claims Merger And Acquisition Related Claims [Member] Merger and acquisition related claims. Counterparty Name Counterparty Name [Axis] Number of shares to be issued upon exercise of outstanding options or vesting of RSUs Share Based Compensation Arrangement By Share Based Payment Award Options And Restricted Stock Units Outstanding Share based compensation arrangement by share based payment award options and restricted stock units outstanding. Common stock, $0.0001 par value; 300,000 shares authorized; 180,091 shares and 176,505 shares issued and outstanding at December 31, 2020 and 2019, respectively Common Stock, Value, Issued Bristol-Myers Squibb BMS Bristol Myers Squibb Company [Member] Bristol-Myers Squibb Company. Increase in aggregate number of shares authorized (in shares) Common Stock, Additional Shares Authorized Common Stock, Additional Shares Authorized Document Fiscal Year Focus Document Fiscal Year Focus MOVANTIK and MOVENTIG M O V A N T I K And M O V E N T I G [Member] MOVANTIK and MOVENTIG. Document Annual Report Document Annual Report Company share of development costs Company Share of Development Costs Company Share of Development Costs Commercial Paper Commercial Paper [Member] Purchase Agreement Share Purchase Agreement [Member] Share purchase agreement. Aggregate Intrinsic Value, exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Settlements Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Neulasta Neulasta [Member] Neulasta. Entity Current Reporting Status Entity Current Reporting Status Partner Two Partner Two [Member] Partner Two Other Liabilities Disclosure [Abstract] Other Liabilities Disclosure [Abstract] Subsequent Event [Table] Subsequent Event [Table] Purchases of investments Payments to Acquire Debt Securities, Available-for-sale Net Income (Loss) Per Share Earnings Per Share, Policy [Policy Text Block] Shares issued under equity compensation plans (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Nektar 214 Nektar 214 [Member] Nektar 214. Weighted Average Grant Date Fair Value, Granted (in dollars 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 Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] License and Collaboration 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 Schedule of Revenue by Major Customers, by Reporting Segments [Table] Schedule of Revenue by Major Customers, by Reporting Segments [Table] Purchase and Sale Agreement 2012 Purchase and Sale Agreement 2012 [Member] Purchase and Sale Agreement 2012 Other Deferred Tax Liabilities, Other Operating lease liabilities Operating Lease, Liability Total deferred tax liabilities Deferred Tax Liabilities, Net Sale of stock consideration received Sale Of Stock Consideration Received Sale of stock consideration received. Segment Reporting [Abstract] Segment Reporting [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Total stockholders’ equity Beginning Balance Ending Balance Stockholders' Equity Attributable to Parent Concentration Risk Type Concentration Risk Type [Domain] Total liabilities and stockholders’ equity Liabilities and Equity Loss Contingencies [Line Items] Loss Contingencies [Line Items] Preferred stock, shares designated (in shares) Preferred Stock Share Designated Preferred stock, shares designated. Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Income Taxes Income Tax Disclosure [Text Block] Proceeds from sale of future royalties, net of $3.8 million of transaction costs Proceeds From Sale of Future Royalties, Net Proceeds From Sale of Future Royalties, Net Entity Address, City or Town Entity Address, City or Town Accrued compensation Employee-related Liabilities, Current Fair Value Hierarchy and NAV Fair Value Hierarchy and NAV [Axis] Restricted Stock Units (RSU) Restricted Stock Units (RSUs) [Member] Share-based compensation plan's share limit reduction for every one restricted stock unit granted (in shares) Share Based Compensation Plans Share Limit For Every One Share Share based compensation plan's share limit for every one share. Lapses in statute of limitations Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Operating lease cost Operating Lease, Cost 2025 Lessee, Operating Lease, Liability, to be Paid, Year Five General and administrative General and Administrative Expense Weighted average antidilutive securities excluded from computation of earnings per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Total Current Current Income Tax Expense (Benefit) Payment of transaction related to purchase and sale agreement Payment of Transaction Related to Purchase and Sale Agreement if Threshold is Achieved Payment of Transaction Related to Purchase and Sale Agreement if Threshold is Achieved Product sales Product Sales Product [Member] Reportable Geographical Components Reportable Geographical Components [Member] Tax positions related to prior year, Additions Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Tax positions related to current year, Additions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Equity Component Equity Component [Domain] Net unrealized gain (loss) on available-for-sale investments OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Operating lease right-of-use assets Deferred Tax Liabilities, Leasing Arrangements Valuation allowance for deferred tax assets Deferred Tax Assets, Valuation Allowance NKTR - 181 NKTR - 181 [Member] NKTR - 181 [Member] Property, plant and equipment, net Property, plant and equipment, net Property, Plant and Equipment, Net Entity Tax Identification Number Entity Tax Identification Number Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Stock-Based Compensation Share-based Payment Arrangement [Text Block] Net income (loss) Net income (loss) Net Income (Loss) Attributable to Parent Milestone [Axis] Milestone [Axis] Milestone [Axis] Changes in operating assets and liabilities Increase (Decrease) in Operating Capital [Abstract] Employee Employee [Member] Employee. Minimum transaction royalties payments needed to pay the difference between the 2025 threshold and 2020 transaction royalties Minimum Transaction Royalties Payments Needed to Pay the Difference Between Thresholds Minimum Transaction Royalties Payments Needed to Pay the Difference Between Thresholds and Transactions Inventory Inventory Disclosure [Text Block] Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Leases [Abstract] Leases [Abstract] Organization and Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Drug Product Development Drug Product Development [Member] Drug product development. Long-term Debt, Type Long-term Debt, Type [Axis] Total current assets Assets, Current Current Fiscal Year End Date Current Fiscal Year End Date Operating leases, net Increase (Decrease) In Operating Lease Right-Of-Use Assets, Net Of Operating Lease Liabilities Increase (Decrease) In Operating Lease Right-Of-Use Assets, Net Of Operating Lease Liabilities Liability related to the sale of future royalties—beginning balance Liability related to the sale of future royalties – ending balance Liability Related To Sale Of Potential Future Royalties Non Current Liability related to sale of potential future royalties noncurrent. Net income (loss) per share Earnings Per Share [Abstract] Significant Components of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Implicit interest rate over the life of the agreement Estimated Annual Interest Rate Over Life Of Royalty Liability Estimated annual interest rate over life of royalty liability. Coronavirus Aid, Relief and Economic Security (CARES) Act Coronavirus Aid, Relief and Economic Security (CARES) Act [Policy Text Block] Coronavirus Aid, Relief and Economic Security (CARES) Act Impairment of assets and other costs for terminated program Impairment of Assets and Other Costs for Terminated Program [Member] Impairment of Assets and Other Costs for Terminated Program Leases [Line Items] Leases [Line Items] Leases [Line Items] Stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Percentage of out-of-pocket costs to be reimbursed by partner Percentage Of Out Of Pocket Costs To Be Reimbursed By Partner Percentage of out of pocket costs to be reimbursed by partner. Level 1 to level 2 transfers Fair Value, Assets, Level 1 to Level 2 Transfers, Amount Cash and Cash Equivalents [Abstract] Cash and Cash Equivalents [Abstract] Proceeds from sale of royalty rights Proceeds From Sale Of Potential Future Royalties Gross Proceeds from sale of potential future royalties gross. Document Fiscal Period Focus Document Fiscal Period Focus Nektar's Parent Company [Member] Impairment of advance payments to contract manufacturers and equipment for terminated program Impairment Of Equipment From Terminated Program Impairment of equipment from terminated program. Certificates of Deposit Certificates of Deposit [Member] Deferred revenue, less current portion Contract with Customer, Liability, Noncurrent Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Entity Filer Category Entity Filer Category 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] Product and Service Product and Service [Domain] Senior secured notes, net and interest payable (see Note 5) Senior Notes, Current Property, Plant and Equipment, Type Long-Lived Tangible Asset [Domain] License, Collaboration and Other Revenue Collaborative Arrangement and Arrangement Other than Collaborative [Table Text Block] Concentration Risk Benchmark Concentration Risk Benchmark [Domain] Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document and entity information. Average volatility factor Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Weighted Average Volatility Rate Compensation expense in connection with 401(k) retirement plan Defined Contribution Plan, Cost Geographic Concentration Risk Geographic Concentration Risk [Member] European Union European Union [Member] Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Lease Contractual Term [Axis] Lease Contractual Term [Axis] Sale of stock to Bristol-Myers Squibb (Note 10) (in shares) Sale of common stock (in shares) Stock Issued During Period, Shares, New Issues Collaborative Arrangements Collaborative Arrangement, Accounting Policy [Policy Text Block] Revenue Revenue Benchmark [Member] Senior secured notes, principal amount Senior Notes Percentage of upfront payment, market access milestone payments, royalties and sales milestone payments from sublicense agreement retained by our collaboration partner Percentage Of Upfront Payment Market Access Milestone Payments Royalties And Sales Milestone Payments From Sublicense Agreement Retained By Our Collaboration Partner Percentage of upfront payment market access milestone payments royalties and sales milestone payments from sublicense agreement retained by our collaboration partner. Royalty monetization proceeds Royalty Monetization Proceeds Proceeds from sale of potential future royalties. Senior secured notes, interest rate Debt Instrument, Interest Rate, Stated Percentage Money Market Funds Money Market Funds [Member] Less: accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Research and other credits Deferred Tax Assets, Tax Credit Carryforwards, Research Number of shares, options exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Purchase and Sale Agreement 2020 Purchase and Sale Agreement 2020 [Member] Purchase and Sale Agreement 2020 Selected Quarterly Financial Data [Table] Selected Quarterly Financial Data [Table] Selected quarterly financial data. Performance obligation recognized Contract with Customer, Performance Obligation Satisfied in Previous Period Accrued interest receivable Interest Receivable, Current Net increase (decrease) in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Total non-operating expense, net Nonoperating Income (Expense) Eli Lilly Eli Lilly [Member] Eli Lilly. Organization And Summary Of Significant Accounting Policies [Table] Organization And Summary Of Significant Accounting Policies [Table] Organization and summary of significant accounting policies. Loss Contingency, Nature Loss Contingency, Nature [Domain] Future Minimum Lease Payments for Operating Leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Shares of Common Stock Underlying Outstanding Stock Options Stock Options Share-based Payment Arrangement, Option [Member] Other accrued expenses Increase (Decrease) in Other Accrued Liabilities Other Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Operating costs and expenses: Costs and Expenses [Abstract] Average risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Subsequent Events [Abstract] Subsequent Events [Abstract] Weighted-Average Exercise Price per Share, options forfeited and canceled (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Net foreign currency translation gain (loss) Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Sale of Stock Sale of Stock [Domain] State Deferred State and Local Income Tax Expense (Benefit) Loss Contingencies [Table] Loss Contingencies [Table] Domestic Income (Loss) from Continuing Operations before Income Taxes, Domestic Plan Name Plan Name [Domain] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Cash paid for interest Interest Paid, Excluding Capitalized Interest, Operating Activities Milestone One Milestone One [Member] Milestone One [Member] Operating lease right-of-use assets recognized in exchange for lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Unrecognized tax benefits, period may increase or decrease due to tax examination Unrecognized Tax Benefits Period Increase (Decrease) Reasonable Period Of Change Unrecognized tax benefits, period increase (decrease) reasonable period of change Cash, Cash Equivalents, and Investments in Marketable Securities Cash and Cash Equivalents, Policy [Policy Text Block] Third Street Lease Third Street Lease [Member] Third street lease. Provision for income taxes Provision for income taxes Income Tax Expense (Benefit) Depreciable property, plant and equipment at cost Depreciable Property Plant And Equipment Gross Depreciable Property, plant and equipment, Gross. Cash paid for income taxes Income Taxes Paid, Net Cash and cash equivalents at beginning of year Cash and cash equivalents at end of year Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Long-Lived Assets Property, Plant and Equipment, Policy [Policy Text Block] Relationship to Entity [Domain] Title of Individual [Domain] Diluted (in dollars per share) Earnings Per Share, Diluted Sales of investments Proceeds from Sale of Debt Securities, Available-for-sale Local Phone Number Local Phone Number Level 2 to level 1 transfers Fair Value, Assets, Level 2 to Level 1 Transfers, Amount Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] Type of Arrangement and Non-arrangement Transactions Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Total intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Payment made for milestone not achieved year two Payment Made For Milestone Not Achieved Year Two Payment made for milestone not achieved year two. Regulatory milestones payment, description Regulatory Milestones Payment Description Regulatory milestones payment description. Sales milestone revenue Sales Milestone Revenue Sales milestone revenue. Payment made for milestone not achieved year one Payment Made For Milestone Not Achieved Year One Payment made for milestone not achieved year one. Entity Address, Address Line One Entity Address, Address Line One Reductions Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Non-cash royalty revenue related to sale of future royalties Non Cash Royalty Revenue Related To Sale Of Future Royalties [Member] Non-cash royalty revenue related to sale of future royalties. Unrecognized tax benefits, interest recognized Unrecognized Tax Benefits, Interest on Income Taxes Expense Success-based payments, second indication Collaborative Arrangement, Success-based Payments, Second Indication Collaborative Arrangement, Success-based Payments, Second Indication Deferred revenue Deferred revenue, Beginning balance Deferred revenue, Ending balance Contract with Customer, Liability Other assets Increase (Decrease) in Other Operating Assets Accretion of premiums (discounts), net and other non-cash transactions Accretion Of Discount Net And Other Non Cash Transactions Accretion of discount net and other non-cash transactions. Entity Emerging Growth Company Entity Emerging Growth Company Income Taxes Disclosure [Line Items] Income Taxes Disclosure [Line Items] Income taxes disclosure. Total Deferred Deferred Income Tax Expense (Benefit) Award Type Award Type [Axis] Lease Contractual Term [Domain] Lease Contractual Term [Domain] Fair value of restricted stock vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Maximum Maximum Maximum [Member] Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Bempegaldesleukin Bempegaldesleukin [Member] Bempegaldesleukin Stock-based compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Prospective effective interest rate Prospective Interest Rate Percentage Prospective interest rate percentage. Accumulated Deficit Retained Earnings [Member] Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Advance payments to contract manufacturers Advance Payments To Contract Manufacturers Amount of advance payments to contract manufacturers, net of amortization. Change in control severance payment period for executives Change In Control Severance Payment Period For Executives Change in control severance payment period for executives. 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] Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Weighted-Average Remaining Contractual Life, outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Percentage of funding phase 3 development costs on an indication by indication basis borne Percentage Of Funding Phase Three Development Costs On An Indication By Indication Basis Borne Percentage of funding Phase three development costs on an indication by indication basis borne. Equity Award Award Type [Domain] Unrecognized tax benefits, penalties recognized Unrecognized Tax Benefits, Income Tax Penalties Expense Reimbursement recognized Reimbursement Recognized Reimbursement Recognized Investments Investments [Domain] Corporate Notes and Bonds Corporate Debt Securities [Member] Trading Symbol Trading Symbol Weighted-Average Exercise Price per Share, exercisable (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Property, Plant and Equipment Property, Plant and Equipment Disclosure [Text Block] Baxalta Incorporated / Takeda Baxalta Incorporated / Takeda Baxalta Incorporated Or Takeda P L C [Member] Baxalta Incorporated or takeda PLC. Change in control severance payment period for employees Change In Control Severance Payment Period For Employees Change in control severance payment period for employees. Manufacturing equipment Manufacturing Laboratory And Other Equipment [Member] Manufacturing laboratory and other equipment. Lease space (in sq ft) Area Of Leased Space Area of leased space. Nektar-358 Nektar-358 [Member] Nektar-358 Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities, Current [Abstract] Selected Quarterly Financial Data [Line Items] Selected Quarterly Financial Data [Line Items] Selected quarterly financial data. Statutory income tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Foreign Income (Loss) from Continuing Operations before Income Taxes, Foreign Entity Shell Company Entity Shell Company Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Other Deferred Tax Assets Depreciation Property And Equipment Deferred tax assets depreciation property and equipment. Recently Adopted Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Entity Public Float Entity Public Float Statement of Financial Position [Abstract] Statement of Financial Position [Abstract]