v3.26.1
Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Commission revenue by fee type    
Revenues $ 233,380 $ 208,576
Commissions [Member]    
Commission revenue by fee type    
Disclosed trading 104,724 95,455
Open Trading - matched principal trading 49,230 43,052
Other Variable Transaction 10,697 4,955
Total variable transaction fees 169,966 147,991
Distribution fees and unused minimum fees 33,505 33,352
Revenues 203,471 181,343
Commissions [Member] | US Government Bonds [Member]    
Commission revenue by fee type    
Open Trading - matched principal trading $ 5,315 $ 4,529