Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Commission revenue by fee type
Revenues	$ 752,547	$ 718,300	$ 698,951
Commissions [Member]
Commission revenue by fee type
Disclosed trading	323,038	321,603	333,712
Matched principal trading	178,517	175,440	155,465
Other Variable Transaction	4,979
Total variable transaction fees	521,756	514,021	501,577
Distribution fees and unused minimum fees	141,208	127,162	119,431
Revenues	662,964	641,183	621,008
Commissions [Member] | US Government Bonds [Member]
Commission revenue by fee type
Matched principal trading	$ 15,222	$ 16,978	$ 12,400