Organization and Summary of Significant Accounting Policies (Details) shares in Millions			1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 14, 2020 USD ($)	Jul. 23, 2017	Apr. 30, 2022	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) reporting_unit shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Mar. 31, 2022 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities					$ 504,977,000	$ 798,783,000
Net expense reimbursements from collaboration partner						21,400,000
Number of reporting unit evaluated for goodwill | reporting_unit					1
Total revenue					$ 92,055,000	101,907,000	$ 152,915,000
Level 3 | Development Derivative Liability
Organization And Summary Of Significant Accounting Policies [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value					$ 0	$ 27,726,000	$ 0	$ 0
Employee Severance
Organization And Summary Of Significant Accounting Policies [Line Items]
Percent of positions eliminated			70.00%
Expense recognized during the period				$ 30,904,000
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					21.2	18.4	17.4
BMS Collaboration Agreement
Organization And Summary Of Significant Accounting Policies [Line Items]
Sales milestone revenue						$ 50,000,000
Nektar-358 | Nektar's | Eli Lilly And Company
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of regulatory milestones payments will be reduced if conditions occur		75.00%
Cash And NonCash Royalties
Organization And Summary Of Significant Accounting Policies [Line Items]
Total revenue					$ 69,800,000	$ 77,700,000	$ 79,600,000
NKTR - 181 | Program Termination
Organization And Summary Of Significant Accounting Policies [Line Items]
Expense recognized during the period	$ 45,200,000
NKTR - 181 | Program Termination, Advance Paymnt To Contract Manyfacturers
Organization And Summary Of Significant Accounting Policies [Line Items]
Expense recognized during the period	19,700,000
NKTR - 181 | Program Termination, Noncancellable Commitments
Organization And Summary Of Significant Accounting Policies [Line Items]
Expense recognized during the period	$ 25,500,000
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 | Nektar-358 | Nektar's | Eli Lilly And Company
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne		25.00%
Maximum | Manufacturing equipment
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives					10 years