Segments - Summary of the Segment Profit or Loss, Including Significant Segment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2026	Mar. 31, 2026	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Jun. 30, 2025
Segment Reporting [Line Items]
Salaries and benefits	$ 9,787		$ 17,863		$ 17,342	$ 29,476
General corporate activities	8,235		16,694		13,209	21,863
Other segment items	24,403		1,308,454		218,063	1,311,145
Segment expenses	62,810		1,573,669		282,392	1,606,155
Net loss	(62,810)	$ (219,582)	(1,573,669)	$ (32,486)	(282,392)	(1,606,155)
Telitacicept - gMG
Segment Reporting [Line Items]
External research and development expenditures	12,152				21,945
Telitacicept - SjD
Segment Reporting [Line Items]
External research and development expenditures	6,331				8,830
Trem-cel
Segment Reporting [Line Items]
External research and development expenditures	0		3,095		250	9,477
VCAR33
Segment Reporting [Line Items]
External research and development expenditures	0		2,419		73	6,055
Other Research and Development
Segment Reporting [Line Items]
External research and development expenditures	$ 1,902		$ 225,144		$ 2,680	$ 228,139