Collaboration Agreements - Summary of Activity and Reimbursement Amounts Related to Collaboration Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue		$ 41,243	$ 86,455	$ 7,686
Research and development expenses		225,895	356,235	326,163
Selling, general and administrative expenses		216,420	274,524	227,699
Collaboration Revenue - Related Party [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue		36,087	824
Biogen Collaboration Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue					$ 1,100,000
Cost of revenues		5,428	504
Research and development expenses		20,617	94,325	86,028
Selling, general and administrative expenses		58,950	89,599	51,870
Reimbursement amounts to (from) collaboration [Abstract]
Collaboration revenue - related party	$ 8,000	(36,087)	(824)
Cost of revenues		(2,723)	504
Selling, general and administrative expenses		10,881	16,496	(2,230)
Biogen Collaboration Agreement [Member] | Research and Development [Member]
Reimbursement amounts to (from) collaboration [Abstract]
Research and development expenses		(15,680)	(76,208)	$ (73,227)
Biogen Collaboration Agreement [Member] | Collaboration Revenue - Related Party [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue		$ 36,087	$ 824