Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Commission revenue by fee type
Revenues	$ 817,097	$ 752,547	$ 718,300
Commissions [Member]
Commission revenue by fee type
Disclosed trading	361,252	323,038	321,603
Open Trading - matched principal trading	177,966	178,517	175,440
Other Variable Transaction	20,016	4,979	0
Total variable transaction fees	578,544	521,756	514,021
Distribution fees and unused minimum fees	133,166	141,208	127,162
Revenues	711,710	662,964	641,183
Commissions [Member] | US Government Bonds [Member]
Commission revenue by fee type
Open Trading - matched principal trading	$ 19,310	$ 15,222	$ 16,978