Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Commission revenue by fee type
Revenues	$ 718,300	$ 698,951	$ 689,125
Commissions [Member]
Commission revenue by fee type
Disclosed trading	321,603	333,712	343,427
Matched principal trading	175,440	155,465	170,537
Total variable transaction fees	514,021	501,577	526,337
Distribution fees and unused minimum fees	127,162	119,431	108,108
Revenues	641,183	621,008	634,445
Commissions [Member] | US Government Bonds [Member]
Commission revenue by fee type
Matched principal trading	$ 16,978	$ 12,400	$ 12,372