Revenues from Contracts with Customers - Summary of Revenues from Contracts with Customers and Other Sources of Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	$ 434,971	$ 384,638	$ 888,584	$ 795,459
Principal transactions	98,439	94,883	211,288	209,812
Interest and dividend income	17,145	13,371	26,909	18,686
Other revenues	206	188	2,594	1,990
Total revenues	550,761	493,080	1,129,375	1,025,947
Commissions
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	395,081	348,720	810,253	726,008
Data, network and post-trade
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	30,812	27,000	61,715	54,122
Fees from related parties
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	4,643	4,062	9,064	8,019
Other revenues
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	4,435	4,856	7,552	7,310
Total revenues	$ 57,241	$ 49,477	$ 107,834	$ 90,127