Segment Reporting - Schedule of Revenue from External Customers by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 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	$ 238,946	$ 1,214	$ 238,917	$ 4,246
U.S. \| Astellas
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	239,276	0	239,276	0
U.S. \| Other
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	11	183	23	1,421
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	$ (341)	$ 1,031	$ (382)	$ 2,825