Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Commission revenue by fee type
Revenues	$ 846,268	$ 817,097	$ 752,547
Commissions [Member]
Commission revenue by fee type
Disclosed trading	376,599	361,252	323,038
Open Trading - matched principal trading	175,557	177,966	178,517
Other Variable Transaction	30,263	20,016	4,979
Total variable transaction fees	600,448	578,544	521,756
Distribution fees and unused minimum fees	134,175	133,166	141,208
Revenues	734,623	711,710	662,964
Commissions [Member] | US Government Bonds [Member]
Commission revenue by fee type
Open Trading - matched principal trading	$ 18,029	$ 19,310	$ 15,222