Cash and Cash Equivalents and Restricted Cash - Summary of Reconciliation of Cash and Cash Equivalents with Restricted or Segregated Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	$ 376,679	$ 451,280
Cash segregated under federal regulations	45,629	45,122
Deposits with clearing organizations and broker-dealers	112,713	115,151
Total	535,164	611,672
Cash and Cash Equivalents [Member]
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	376,679	451,280
Cash Segregated under Federal Regulations [Member]
Cash And Cash Equivalents [Line Items]
Cash segregated under federal regulations	45,629	45,122
Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]
Cash And Cash Equivalents [Line Items]
Deposits with clearing organizations and broker-dealers	112,713	115,151
Prepaid Expenses and Other Assets [Member]
Cash And Cash Equivalents [Line Items]
Other deposits	$ 143	$ 119