Restructuring, Impairment and Costs of Terminated Program - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended								9 Months Ended	12 Months Ended			21 Months Ended
	Jan. 31, 2024	Jun. 30, 2023	Jan. 31, 2023	Apr. 30, 2022	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2023
Restructuring Cost and Reserve [Line Items]
Non-cash impairment charges														$ 36,962	$ 67,875
Impairment of goodwill								$ 76,500						76,501	0	$ 0
Nektar 214 | Bristol-Myers Squibb Company
Restructuring Cost and Reserve [Line Items]
Reimbursement of expenses													$ 20,800		20,800
Nektar 214 | Research and Development Expense | Bristol-Myers Squibb Company
Restructuring Cost and Reserve [Line Items]
Reimbursement of expenses												$ 24,900			45,700	$ 101,500
2022 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Non-cash impairment charges					$ 0	$ (1,467)	$ (13,261)	0	$ (12,361)	$ (1,200)	$ (52,200)						$ (80,489)
Contract termination and other costs included in accrued expenses					$ 3,000									3,000			$ 3,000
2023 Restructuring Plan | Life Sciences Lease Market
Restructuring Cost and Reserve [Line Items]
Non-cash impairment charges						$ 9,100
2023 Restructuring Plan | Office and Laboratory Space | Mission Bay Facility
Restructuring Cost and Reserve [Line Items]
Non-cash impairment charges								$ 11,500						20,600
Measurement Input, Market Participant Subtenant Borrowing Rate | Maximum
Restructuring Cost and Reserve [Line Items]
Operating lease, measurement input						8.70%
Measurement Input, Market Participant Subtenant Borrowing Rate | Minimum
Restructuring Cost and Reserve [Line Items]
Operating lease, measurement input											6.40%
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring, impairment, and costs of terminated program														7,885	30,904
Payments during the period			$ 3,300											10,988	27,605
Employee Severance | 2022 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce termination, percentage				70.00%
Restructuring, impairment, and costs of terminated program														0	30,904
Payments during the period														3,299	27,605
Employee Severance | 2023 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce termination, percentage		60.00%
Restructuring, impairment, and costs of terminated program														7,885	0
Payments during the period														$ 7,689	$ 0
Employee Severance | 2023 Restructuring Plan | Subsequent Event
Restructuring Cost and Reserve [Line Items]
Payments during the period	$ 200