Segment Reporting - Schedule of Revenue from External Customers by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Total segment and consolidated revenue	$ (188)	$ 240	$ 238,729	$ 4,486
Foreign
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Total segment and consolidated revenue	(214)	(65)	(596)	2,760
Astellas \| U.S.
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Total segment and consolidated revenue	0	0	239,276	0
Other \| U.S.
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Line Items]
Total segment and consolidated revenue	$ 26	$ 305	$ 49	$ 1,726