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Document Fiscal Period Focus Document Fiscal Period Focus Cost of goods sold Cost of Goods and Services Sold Operating Lease Right-of-Use Assets Sublease Operating Lease Right of Use Assets [Member] Sublease Operating Lease Right of Use Assets Clinical trial expense, other third-party and employee costs for the wind down of the bempegaldesleukin program Business Exit Costs Weighted average shares outstanding used in computing diluted net loss per share (in shares) Weighted Average Number of Shares Outstanding, Diluted Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Less: accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Derivative liability Derivative Liability Loss Contingency, Nature Loss Contingency, Nature [Domain] Inventory Schedule of Inventory, Current [Table Text Block] Investments, fair value disclosure Investments, Fair Value Disclosure Depreciable property, plant and equipment, net Total Property Plant And Equipment Excluding Construction In Progress [Member] Total Property Plant And Equipment Excluding Construction In Progress Depreciable property, plant and equipment at cost Property, Plant and Equipment, Gross Potential future additional development and regulatory milestones (up to) Potential Development And Regulatory Milestones Potential development and regulatory milestones. 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Amortization of premiums (discounts), net and other non-cash transactions Other Noncash Income (Expense) Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Current liabilities: Liabilities, Current [Abstract] Non-cash research and development expense Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Research and Development Expense Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Research and Development Expense Net loss Net loss Net Income (Loss) Attributable to Parent Measurement Input Type [Domain] Measurement Input Type [Domain] License, collaboration and other revenue License Collaboration And Other Revenue [Member] License collaboration and other revenue. Potentially dilutive securities (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Income Statement Location [Domain] Income Statement Location [Domain] 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] Equity Component Equity Component [Domain] Amendment Flag Amendment Flag Net cash provided by investing activities Net Cash Provided by (Used in) Investing Activities Cash And Investments In Marketable Securities [Table] Cash And Investments In Marketable Securities [Table] Cash and Investments in Marketable Securities [Table] Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Comprehensive loss Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Percentage of sharing in Phase 2 development costs Percentage Of Sharing In Phase Two Development Costs Percentage of sharing in Phase 2 development costs. 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Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Computer equipment and software Computer Equipment And Software [Member] Computer Equipment And Software Maximum Maximum [Member] Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Liabilities related to the sales of future royalties, net Liabilities related to the sales 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. 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Revenue: Revenues [Abstract] Restructuring, impairment and other costs of terminated program Restructuring, Impairment And Other Costs Of Terminated Program [Member] Restructuring, Impairment And Other Costs Of Terminated Program Restructuring Type [Axis] Restructuring Type [Axis] Impairment expense for facilities Impairment of Leasehold Severance and benefit expense Severance Costs Schedule of Portfolio of Cash and Investments in Marketable Securities Fair Value, Assets Measured on Recurring Basis [Table Text Block] Purchases of investments Payments to Acquire Debt Securities, Available-for-Sale Product and Service [Domain] Product and Service [Domain] Entity Shell Company Entity Shell Company Payments to RPI Partial Repayment Of Royalty Sale Proceeds Partial Repayment Of Royalty Sale Proceeds Nektar 214 Nektar 214 [Member] Nektar 214. Organization Organization Policy [Text Block] Organization. Liabilities Related to Sales of Future Royalties Liability Related To Sale Of Potential Future Royalties [Text Block] Liability related to sale of potential future royalties. Laboratory equipment Laboratory Equipment [Member] Laboratory Equipment Long-Lived Tangible Asset [Domain] Long-Lived Tangible Asset [Domain] Financial Instrument [Axis] Financial Instrument [Axis] Accounts receivable Increase (Decrease) in Accounts Receivable Title of 12(b) Security Title of 12(b) Security 2012 Purchase and Sale Agreement Purchase and Sale Agreement 2012 [Member] Purchase and Sale Agreement 2012 Consolidated Entities [Axis] Consolidated Entities [Axis] Document Period End Date Document Period End Date Sale of stock consideration received Sale Of Stock Consideration Received Sale of stock consideration received. 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Earnings Per Share [Abstract] Earnings Per Share [Abstract] Preferred stock, shares designated (in shares) Preferred Stock Share Designated Preferred stock, shares designated. Other accrued expenses Increase (Decrease) in Other Accrued Liabilities Income Statement Location [Axis] Income Statement Location [Axis] Accrued clinical trial expenses Accrued Clinical Trial Expenses Current Accrued clinical trial expenses current. LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities and Equity [Abstract] Estimate of Fair Value Measurement Estimate of Fair Value Measurement [Member] Shares issued (in shares) Shares, Issued Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Amortized Cost Debt Securities, Available-for-Sale, Amortized Cost Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Cash and Investments in Marketable Securities Cash, Cash Equivalents, and Marketable Securities [Text Block] Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Inventory Total inventory Inventory, Net Weighted average maturity term for debt securities investment (or less) Debt Investment Maturity Term Debt investment maturity date description. 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Cover [Abstract] Fair Value, Level 3 Fair Value, Inputs, Level 3 [Member] Results of Bempegaldesleukin Program and the Restructuring Plan Costs Associated with Exit or Disposal Activity or Restructuring [Policy Text Block] Basis of Presentation and Principles of Consolidation Consolidation, Policy [Policy Text Block] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Long-term investments Debt Securities, Available-for-Sale, Noncurrent Stock-Based Compensation Share-Based Payment Arrangement [Text Block] Restructuring and Related Activities [Abstract] Asset Class [Domain] Asset Class [Domain] Work-in-process Inventory, Work in Process, Net of Reserves Minimum Minimum [Member] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Entity Emerging Growth Company Entity Emerging Growth Company Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Raw materials Inventory, Raw Materials, Net of Reserves Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Total liabilities and stockholders’ equity Liabilities and Equity Trading Symbol Trading Symbol Entity File Number Entity File Number Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Proceeds from shares issued under equity compensation plans Proceeds, Issuance of Shares, Share-Based Payment Arrangement, Excluding Option Exercised Cash Cash Research and development Research and Development Expense Schedule Of Liability Related To Sale Of 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 Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Manufacturing equipment Equipment [Member] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Cash receipts from SFJ Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Issuances Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Level 2 Fair Value, Inputs, Level 2 [Member] RSUs granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Restricted Stock Units (RSU) Restricted Stock Units (RSUs) [Member] Current Fiscal Year End Date Current Fiscal Year End Date Diluted net loss per share (in dollars per share) Earnings Per Share, Diluted Sale of Stock [Domain] Sale of Stock [Domain] Use of Estimates Use of Estimates, Policy [Policy Text Block] No service period Employee Severance With No Service Period [Member] Employee Severance With No Service Period SFJ SFJ Pharmaceuticals [Member] SFJ Pharmaceuticals Nektar's Parent Company [Member] Accounts payable Increase (Decrease) in Accounts Payable Organization and Summary of Significant Accounting Policies Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Stock-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Fair value at beginning of period Fair value at end of period Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Success payments (up to) Collaborative Arrangement, Success-Based Payments, Amount Collaborative Arrangement, Success-Based Payments, Amount Building and leasehold improvements Building and Leasehold Improvements [Member] Building and Leasehold Improvements Liability Related To Sale Of Future Royalties [Table] Liability Related To Sale Of Future Royalties [Table] Liability related to sale of future royalties. 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Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Entity Tax Identification Number Entity Tax Identification Number Aggregate number of shares authorized (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized Royalties liability discount rate Royalties Liability, Measurement Input Royalties Liability, Measurement Input Common Shares Common Stock [Member] Schedule of Stock-Based Compensation Expense Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Shares issued under equity compensation plans Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Restructuring Costs Associated with Exit or Disposal Activities or Restructurings, Policy [Policy Text Block] Reimbursement of expenses Reimbursement Of Expenses Reimbursement of expenses. 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