Cash and Cash Equivalents and Restricted Cash - Summary of Reconciliation of Cash and Cash Equivalents with Restricted or Segregated Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	$ 473,299	$ 544,478
Cash segregated for regulatory purposes	48,351	47,107
Total	642,774	700,459
Cash and Cash Equivalents [Member]
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	473,299	544,478
Cash Segregated under Federal Regulations [Member]
Cash And Cash Equivalents [Line Items]
Cash segregated for regulatory purposes	48,351	47,107
Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]
Cash And Cash Equivalents [Line Items]
Restricted cash deposits with clearing organizations and broker-dealers	119,942	107,652
Prepaid Expenses and Other Assets [Member]
Cash And Cash Equivalents [Line Items]
Other restricted cash deposits	$ 1,182	$ 1,222