Cash and Cash Equivalents and Restricted Cash - Summary of Reconciliation of Cash and Cash Equivalents with Restricted or Segregated Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	$ 451,280	$ 430,746
Cash segregated under federal regulations	45,122	50,947
Deposits with clearing organizations and broker-dealers	115,151	88,923
Total	611,672	572,664	$ 625,567
Cash and Cash Equivalents [Member]
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	451,280	430,746	506,735
Cash Segregated under Federal Regulations [Member]
Cash And Cash Equivalents [Line Items]
Cash segregated under federal regulations	45,122	50,947	50,159
Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]
Cash And Cash Equivalents [Line Items]
Deposits with clearing organizations and broker-dealers	115,151	88,923	68,565
Prepaid Expenses and Other Assets [Member]
Cash And Cash Equivalents [Line Items]
Other deposits	$ 119	$ 2,048	$ 108