Restructuring, Impairment and Costs of Terminated Program, and Impairment of Goodwill - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended				6 Months Ended		12 Months Ended	18 Months Ended
	Jan. 31, 2023	Apr. 30, 2022	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022	Jun. 30, 2023
Restructuring Cost and Reserve [Line Items]
Impairment expense for facilities			$ 13,255	$ 11,500		$ 52,201	$ 24,755	$ 52,200
Impairment of other property, plant and equipment				1,700		5,120	1,700
Impairment of goodwill			0	$ 76,500		0	76,501	0
Impairment of other property, plant and equipment			13,300			57,321	26,455	57,321
Nektar 214 | Research and Development Expense | Bristol Myers Squibb Company
Restructuring Cost and Reserve [Line Items]
Reimbursement of expenses						7,600		24,900
Third St. Facility
Restructuring Cost and Reserve [Line Items]
Impairment expense for facilities			6,200		$ 12,000
Mission Bay Facility
Restructuring Cost and Reserve [Line Items]
Impairment expense for facilities			7,100
2022 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Contract termination and other restructuring costs			0			566	878	2,041		$ 11,800
Impairment of other property, plant and equipment			13,255			$ 57,321	13,255	$ 57,321
2023 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Contract termination and other restructuring costs			0				34
Impairment of other property, plant and equipment			$ 0				$ 13,200
Measurement Input, Market Participant Subtenant Borrowing Rate
Restructuring Cost and Reserve [Line Items]
Operating lease, measurement input				7.90%		6.40%
Sublease income, measurement input			8.50%
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring, impairment, and costs of terminated program			$ 1,943	$ 5,483					$ 30,900
Payments during the period	$ 3,300		6,624	3,299
Employee Severance | 2022 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce termination, percentage		70.00%
Restructuring, impairment, and costs of terminated program			0	0
Payments during the period			0	3,299
Employee Severance | 2023 Restructuring Plan
Restructuring Cost and Reserve [Line Items]
Workforce termination, percentage							60.00%
Restructuring, impairment, and costs of terminated program			1,943	5,483
Payments during the period			$ 6,624	$ 0