v3.26.1
Commitments and Contingencies - Summary of Expenses Incurred by Company (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Cost of License and Royalty Revenues [Abstract]        
Royalties on net sales of Zolgensma and Itvisma $ 108,019 $ 21,359 $ 114,412 $ 110,371
GlaxoSmithKline LLC [Member]        
Other Commitments [Line Items]        
Total related party transaction expense 944 5,262 12,028 8,136
GlaxoSmithKline LLC [Member] | Zolgensma Royalties Itvisma [Member]        
Cost of License and Royalty Revenues [Abstract]        
Royalties on net sales of Zolgensma and Itvisma 760 5,204 1,809 7,786
GlaxoSmithKline LLC [Member] | Location, Statement of Income, Balance [Axis]: us-gaap:GeneralAndAdministrativeExpense        
Other Commitments [Line Items]        
Total related party transaction expense 48 53 79 107
GlaxoSmithKline LLC [Member] | Settlement Payment [Member]        
Other Commitments [Line Items]        
Total related party transaction expense     10,000  
GlaxoSmithKline LLC [Member] | Other [Member]        
Other Commitments [Line Items]        
Total related party transaction expense 136 5 140 243
GlaxoSmithKline LLC [Member] | Cost of License and Royalty Revenues [Member]        
Other Commitments [Line Items]        
Total related party transaction expense $ 896 $ 5,209 $ 11,949 $ 8,029