v3.26.3
Commitments and Contingencies - Summary of Expenses Incurred by Company (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Cost of License and Royalty Revenues [Abstract]        
Royalties on net sales of Zolgensma and Itvisma $ 9,162 $ 29,733 $ 123,574 $ 140,104
GlaxoSmithKline LLC [Member]        
Other Commitments [Line Items]        
Total related party transaction expense 840 5,740 12,868 13,876
GlaxoSmithKline LLC [Member] | Zolgensma Royalties Itvisma [Member]        
Cost of License and Royalty Revenues [Abstract]        
Royalties on net sales of Zolgensma and Itvisma 869 5,709 2,678 13,495
GlaxoSmithKline LLC [Member] | Location, Statement of Income, Balance [Axis]: us-gaap:GeneralAndAdministrativeExpense        
Other Commitments [Line Items]        
Total related party transaction expense (29) 30 50 137
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   1 140 244
GlaxoSmithKline LLC [Member] | Cost of License and Royalty Revenues [Member]        
Other Commitments [Line Items]        
Total related party transaction expense $ 869 $ 5,710 $ 12,818 $ 13,739