License and Collaboration Agreements - Additional Information (Details) - USD ($)				1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 12, 2021	Apr. 03, 2018	Jul. 23, 2017	Apr. 30, 2018	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Derivative liability									$ 0
Revenue, excluding assessed tax					$ 20,499,000	$ 21,585,000	$ 42,093,000	$ 46,407,000
SFJ
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Committed funding (up to)	$ 150,000,000
Success payments (up to)	$ 637,500,000
Non-cash royalty revenue related to the sales of future royalties
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue, excluding assessed tax					15,832,000	16,264,000	32,693,000	33,825,000
Bristol Myers Squibb Company | 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 Company | Nektar 214 | Research and Development Expense
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement of expenses						$ 7,600,000		$ 24,900,000
Other Partner
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones					$ 40,000,000		$ 40,000,000
Nektar-358 | Eli Lilly
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing in Phase 2 development costs			75.00%
Nektar-358 | Maximum | Eli Lilly And Company
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional development and regulatory milestones (up to)			$ 250,000,000
Bristol Myers Squibb Collaboration Agreement | Bristol Myers Squibb Company | Nektar 214
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing production costs		35.00%
Bristol Myers Squibb Collaboration Agreement | Bristol Myers Squibb Company | Nektar 214 | Opdivo
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs		67.50%
Nektar's | Nektar-358
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%
Nektar's | Bristol Myers Squibb Collaboration Agreement | Nektar 214
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing production costs		65.00%
Upfront and milestone payments received from license agreements				$ 1,000,000,000
Nektar's | Bristol Myers Squibb Collaboration Agreement | Nektar 214 | Milestone One
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones										$ 50,000,000
Nektar's | Bristol Myers Squibb Collaboration Agreement | Nektar 214 | Opdivo
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs		32.50%