Revenues from Contracts with Customers - Summary of Revenues from Contracts with Customers and Other Sources of Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	$ 410,821	$ 387,401
Principal transactions	114,929	115,601
Interest and dividend income	5,315	2,435
Other revenues	1,802	1,027
Total revenues	532,867	506,464
Commissions
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	377,288	356,664
Data, software, and post-trade
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	27,122	24,127
Fees from related parties
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	3,957	3,317
Other revenues
Revenues From Contracts With Customers [Line Items]
Revenues from contracts with customers:	2,454	3,293
Total revenues	$ 40,650	$ 34,199