Organization and Summary of Significant Accounting Policies (Details) shares in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) reporting_unit shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities	$ 798,783,000				$ 1,198,558,000				$ 798,783,000	$ 1,198,558,000
Net expense reimbursements from collaboration partner									$ 21,400,000	38,700,000
Number of reporting unit evaluated for goodwill | reporting_unit									1
Total revenue	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
Purchase commitments related to contract manufacturing, clinical development and certain other items	$ 8,200,000								$ 8,200,000
BMS Collaboration Agreement
Organization And Summary Of Significant Accounting Policies [Line Items]
Sales milestone revenue										$ 50,000,000
Stock Options, RSUs and PSUs
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share (in shares) | shares									18.4	17.4	17.9
NKTR - 181
Organization And Summary Of Significant Accounting Policies [Line Items]
Write off of prepayment								19,700,000
Purchase commitments related to contract manufacturing, clinical development and certain other items								$ 25,500,000
Non-cash royalty revenue related to the sales of future royalties
Organization And Summary Of Significant Accounting Policies [Line Items]
Total revenue									$ 77,746,000	$ 48,563,000	$ 36,303,000
Cash And NonCash Royalties
Organization And Summary Of Significant Accounting Policies [Line Items]
Total revenue									$ 77,700,000	$ 79,600,000	$ 77,500,000
Buildings
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									20 years
Minimum | Manufacturing equipment
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									3 years
Maximum | Manufacturing equipment
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives									10 years