Collaboration Agreements - Summary of Activity and Reimbursement Amounts Related to Collaboration Agreement (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 7,902	$ 3,294
Research and development expenses	71,734	92,826
Selling, general and administrative expenses	52,574	65,708
Collaboration Revenue - Related Party [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	6,212
Biogen Collaboration Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue				$ 1,100,000
Cost of revenues	1,201
Research and development expenses	7,031	22,171
Selling, general and administrative expenses	12,983	18,963
Reimbursement amounts to (from) collaboration [Abstract]
Collaboration revenue - related party	(6,212)		$ 8,000
Cost of revenues	(562)
Selling, general and administrative expenses	2,306	3,034
Biogen Collaboration Agreement [Member] | Research and Development [Member]
Reimbursement amounts to (from) collaboration [Abstract]
Research and development expenses	(5,657)	$ (17,282)
Biogen Collaboration Agreement [Member] | Collaboration Revenue - Related Party [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 6,212