License and Collaboration Agreements - Additional Information (Details) - USD ($)			1 Months Ended					3 Months Ended								12 Months Ended
	Feb. 13, 2018	Aug. 23, 2017	Apr. 30, 2018	Sep. 30, 2017	Aug. 31, 2017	Mar. 31, 2016	Oct. 31, 2010	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 09, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones								$ 1,700,000,000								$ 1,700,000,000
Accounts receivable								22,492,000				$ 38,889,000				22,492,000	$ 38,889,000
Revenue recognized from contracts with customers								25,009,000	$ 24,921,000	$ 28,330,000	$ 23,647,000	23,462,000	$ 30,033,000	$ 48,847,000	$ 50,573,000	101,907,000	152,915,000	$ 114,617,000
Bristol Myers Squibb Collaboration Agreement | Nektar 214 | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Global commercialization profits and losses sharing percentage	65.00%
Percentage of sharing production costs	65.00%
Upfront and milestone payments received from license agreements			$ 1,000,000,000
Maximum total additional cash payments receivable upon achievement of certain development and regulatory milestones																1,400,000,000
Bristol Myers Squibb Collaboration Agreement | Nektar 214 | Maximum | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Eligible additional cash payments receivable upon achievement of certain sales milestones			$ 350,000,000
Bristol Myers Squibb Collaboration Agreement | Nektar 214 | Opdivo | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	32.50%
Nektar-358 | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment				$ 150,000,000
Percentage of sharing in Phase 2 development costs		25.00%
NKTR-358 | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue								0								0
Nektar
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of upfront payment, market access milestones, royalties and sales milestones						40.00%
Bristol-Myers Squibb | Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shares issued (in shares)			8,284,600
Sale of stock consideration received			$ 850,000,000
Bristol-Myers Squibb | Nektar 214 | Research and Development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement of expenses																101,500,000	128,200,000		$ 105,400,000
Bristol-Myers Squibb | BMS Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accounts receivable								21,400,000				$ 38,700,000				21,400,000	38,700,000
Company share of development costs, annual cap																125,000,000	4,000,000
Bristol-Myers Squibb | Bristol Myers Squibb Collaboration Agreement | Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total consideration received under agreements																			1,850,000,000
Estimated fair value of shares																			790,200,000
Remaining amount allocated to transaction price																	$ 50,000,000		$ 1,059,800,000
Potential future development, regulatory and sales milestones								$ 1,800,000,000								$ 1,800,000,000
Bristol-Myers Squibb | Bristol Myers Squibb Collaboration Agreement | Nektar 214
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Global commercialization profits and losses sharing percentage	35.00%
Percentage of sharing production costs	35.00%
Bristol-Myers Squibb | Bristol Myers Squibb Collaboration Agreement | Nektar 214 | Opdivo
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	67.50%
Eli Lilly and Company | Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation				125,900,000
Revenue recognized from contracts with customers					$ 125,900,000
Eli Lilly and Company | Nektar-358 | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of regulatory milestones payments will be reduced under certain conditions		50.00%
Percentage of regulatory milestones payments will be reduced if conditions occur		75.00%
Eli Lilly and Company | Nektar-358 | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional development and regulatory milestones		$ 250,000,000
Eli Lilly and Company | Nektar-358 | Maximum | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne		25.00%
Eli Lilly and Company | Nektar-358 | Minimum | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne		0.00%
Eli Lilly and Company | Phase 1 Clinical Development | Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation				17,600,000
Eli Lilly and Company | Drug Product Development | Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation				$ 6,500,000
Eli Lilly | Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing in Phase 2 development costs		75.00%
Amgen, Inc.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment							$ 50,000,000
Amgen, Inc. | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue period of recognition								10 years								10 years
Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones								$ 40,000,000								$ 40,000,000
Terminated Partnership
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue								$ 2,000,000								$ 2,000,000
Milestone One | Bristol Myers Squibb Collaboration Agreement | Nektar 214 | Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones																				$ 25,000,000