Segment Reporting - Summary of Significant Expense Categories and Consolidated Net Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Revenue	$ 10,460	$ 21,639
Operating costs and expenses:
Cost of goods sold	0	8,534
Clinical development, contract manufacturing and other third party costs	17,942	15,455
Employee costs	11,974	10,317
Facilities costs	3,358	4,532
Other operating costs	17,260	11,205
Other segment expenses	4,461	7,023
Total operating costs and expenses	54,995	57,066
Loss from operations	(44,535)	(35,427)
Non-operating income (expense):
Non-cash interest expense on liabilities related to the sales of future royalties	(4,974)	(5,531)
Interest income	2,874	4,220
Other income (expense), net	266	(99)
Total non-operating income (expense), net	(1,834)	(1,410)
Loss before provision (benefit) for income taxes and equity method investment	(46,369)	(36,837)
Provision (benefit) for income taxes	52	(35)
Loss before equity method investment	(46,421)	(36,802)
Loss from equity method investment	(4,461)	0
Net loss	(50,882)	(36,802)
Rezpegaldesleukin (cytokine Treg stimulant)
Operating costs and expenses:
Clinical development, contract manufacturing and other third party costs	13,803	8,884
NKTR-255 (IL-15 receptor agonist)
Operating costs and expenses:
Clinical development, contract manufacturing and other third party costs	1,389	3,486
NKTR-0165 (tumor necrosis factor receptor type II agonist)
Operating costs and expenses:
Clinical development, contract manufacturing and other third party costs	2,281	2,018
Discovery Research and Other Programs
Operating costs and expenses:
Clinical development, contract manufacturing and other third party costs	$ 469	$ 1,067