Segments - Summary of the Segment Profit or Loss, Including Significant Segment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2026	Jun. 30, 2026	Mar. 31, 2026	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2026	Sep. 30, 2025
Segment Reporting [Line Items]
Net loss	$ (86,727)	$ (62,810)	$ (219,582)	$ (812,684)	$ (1,573,669)	$ (32,486)	$ (369,119)	$ (2,418,839)
Single Reportable Segment
Segment Reporting [Line Items]
Salaries and benefits	11,940			2,599			29,282	32,075
General corporate activities	8,876			4,093			22,087	25,956
Other segment items	38,268			792,629			256,331	2,103,774
Segment expenses	86,727			812,684			369,119	2,418,839
Net loss	(86,727)			(812,684)			(369,119)	(2,418,839)
Telitacicept - gMG \| Single Reportable Segment
Segment Reporting [Line Items]
External research and development expenditures	17,056			13,069			39,000	13,069
Telitacicept - SjD \| Single Reportable Segment
Segment Reporting [Line Items]
External research and development expenditures	7,848						16,678
Trem-cel \| Single Reportable Segment
Segment Reporting [Line Items]
External research and development expenditures				(102)			250	9,375
VCAR33 \| Single Reportable Segment
Segment Reporting [Line Items]
External research and development expenditures				(60)			73	5,995
Other Research and Development \| Single Reportable Segment
Segment Reporting [Line Items]
External research and development expenditures	$ 2,739			$ 456			$ 5,418	$ 228,595