v3.26.1
Fair Value Measurements - Carrying Value of Financial Asset and Liability Not Measured at Fair Value (Detail) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Financial assets not measured at fair value:    
Financial assets not measured at fair value $ 188,323 $ 195,879
Level 1 [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 17,196 23,355
Level 2 [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 171,127 172,524
Financial Assets and Liabilities not Measured [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 1,514,379 1,135,301
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 924,552 545,959
Financial Assets and Liabilities not Measured [Member] | Payables to Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 696,302 325,959
Financial Assets and Liabilities not Measured [Member] | Borrowings [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 228,250 220,000
Financial Assets and Liabilities not Measured [Member] | Cash [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 360,106 496,379
Financial Assets and Liabilities not Measured [Member] | Cash Segregated under Federal Regulations [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 49,053 48,722
Financial Assets and Liabilities not Measured [Member] | Accounts Receivable, Net of Allowance [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 128,171 100,989
Financial Assets and Liabilities not Measured [Member] | Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 977,049 489,211
Financial Assets and Liabilities not Measured [Member] | Level 1 [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 529,630 652,324
Financial Assets and Liabilities not Measured [Member] | Level 1 [Member] | Cash [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 360,106 496,379
Financial Assets and Liabilities not Measured [Member] | Level 1 [Member] | Cash Segregated under Federal Regulations [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 49,053 48,722
Financial Assets and Liabilities not Measured [Member] | Level 1 [Member] | Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 120,471 107,223
Financial Assets and Liabilities not Measured [Member] | Level 2 [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 984,749 482,977
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 924,552 545,959
Financial Assets and Liabilities not Measured [Member] | Level 2 [Member] | Payables to Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 696,302 325,959
Financial Assets and Liabilities not Measured [Member] | Level 2 [Member] | Borrowings [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 228,250 220,000
Financial Assets and Liabilities not Measured [Member] | Level 2 [Member] | Accounts Receivable, Net of Allowance [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 128,171 100,989
Financial Assets and Liabilities not Measured [Member] | Level 2 [Member] | Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 856,578 381,988
Financial Assets and Liabilities not Measured [Member] | Carrying Value [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 1,514,379 1,135,301
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 924,552 545,959
Financial Assets and Liabilities not Measured [Member] | Carrying Value [Member] | Payables to Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 696,302 325,959
Financial Assets and Liabilities not Measured [Member] | Carrying Value [Member] | Borrowings [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 228,250 220,000
Financial Assets and Liabilities not Measured [Member] | Carrying Value [Member] | Cash [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 360,106 496,379
Financial Assets and Liabilities not Measured [Member] | Carrying Value [Member] | Cash Segregated under Federal Regulations [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 49,053 48,722
Financial Assets and Liabilities not Measured [Member] | Carrying Value [Member] | Accounts Receivable, Net of Allowance [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 128,171 100,989
Financial Assets and Liabilities not Measured [Member] | Carrying Value [Member] | Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 977,049 489,211
Financial Assets and Liabilities not Measured [Member] | Fair Value [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 1,514,379 1,135,301
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 924,552 545,959
Financial Assets and Liabilities not Measured [Member] | Fair Value [Member] | Payables to Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 696,302 325,959
Financial Assets and Liabilities not Measured [Member] | Fair Value [Member] | Borrowings [Member]    
Financial liabilities not measured at fair value:    
Financial liabilities not measured at fair value 228,250 220,000
Financial Assets and Liabilities not Measured [Member] | Fair Value [Member] | Cash [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 360,106 496,379
Financial Assets and Liabilities not Measured [Member] | Fair Value [Member] | Cash Segregated under Federal Regulations [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 49,053 48,722
Financial Assets and Liabilities not Measured [Member] | Fair Value [Member] | Accounts Receivable, Net of Allowance [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value 128,171 100,989
Financial Assets and Liabilities not Measured [Member] | Fair Value [Member] | Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]    
Financial assets not measured at fair value:    
Financial assets not measured at fair value $ 977,049 $ 489,211