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Assets and Liabilities, at Fair Value - Schedule of Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Sep. 30, 2024
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents | $ 309.0 | $ 51.8
Securities and other assets segregated under federal and other regulations | 3,156.6 | 2,841.2
Financial instruments owned | 6,918.1 | 6,767.1
Physical commodities inventory | 861.4 | 681.1
Accounts payable and other accrued liabilities | 441.8 | 522.1
Financial instruments sold, not yet purchased | 3,541.6 | 2,853.3
Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents | 45.8 | 49.2
Securities and other assets segregated under federal and other regulations | 309.0 | 51.8
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 4,781.3 | 3,287.5
Receivables from clients, net - Derivatives | (2.8) | (8.4)
Financial instruments owned | 6,918.1 | 6,767.1
Total assets at fair value | 12,528.1 | 10,523.8
Accounts payable and other accrued liabilities | 2.9 |
Payables to clients - Derivatives | 371.1 | 265.9
Total liabilities at fair value | 3,953.1 | 3,120.1
Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 15.9 | 1.5
Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 21.6 | (2.9)
Fair Value, Recurring | Payable to broker-dealers, clearing organizations and counterparties |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 37.5 | (1.4)
Fair Value, Recurring | Accounts payable and other accrued liabilities - contingent liabilities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Accounts payable and other accrued liabilities |  | 2.3
Fair Value, Recurring | Physical commodities inventory |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 476.7 | 376.6
Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 623.7 | 1,088.6
Financial instruments sold, not yet purchased | 2,583.2 | 2,139.3
Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.8 | 41.4
Financial instruments sold, not yet purchased | 0.8 | 41.0
Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 226.0 | 228.1
Financial instruments sold, not yet purchased | 288.9 | 264.8
Fair Value, Recurring | Equity securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 540.3 | 378.9
Financial instruments sold, not yet purchased | 429.8 | 224.8
Fair Value, Recurring | Corporate and municipal bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 475.6 | 322.1
Financial instruments sold, not yet purchased | 230.3 | 154.6
Fair Value, Recurring | U.S. government agency obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 488.7 | 531.0
Financial instruments sold, not yet purchased | 0.2 | 0.2
Fair Value, Recurring | Agency mortgage-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 4,197.1 | 3,837.2
Financial instruments sold, not yet purchased | 1.7 | 23.6
Fair Value, Recurring | Asset-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 265.5 | 223.5
Financial instruments sold, not yet purchased | 5.0 | 3.9
Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 61.0 | 67.8
Fair Value, Recurring | Exchange firm common stock |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 13.9 | 13.2
Fair Value, Recurring | Cash flow hedges |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 1.2 | 9.6
Financial instruments sold, not yet purchased | 0.9 | 0.2
Fair Value, Recurring | Mutual funds and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 24.3 | 25.7
Fair Value, Recurring | Other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments sold, not yet purchased | 0.8 | 0.9
Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 49.3 | 7.8
Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 16.7 | 18.3
Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 4,241.5 | 2,933.2
Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 473.8 | 328.2
Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 9.1 | 51.8
Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 299.9 |
Fair Value, Recurring | Netting |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents | 0.0 | 0.0
Securities and other assets segregated under federal and other regulations | 0.0 | 0.0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | (6,047.5) | (5,758.4)
Receivables from clients, net - Derivatives | (495.3) | (537.0)
Financial instruments owned | (593.2) | (375.2)
Total assets at fair value | (7,136.0) | (6,670.6)
Accounts payable and other accrued liabilities | 0.0 |
Payables to clients - Derivatives | (3,271.1) | (3,540.1)
Financial instruments sold, not yet purchased | (513.2) | (314.3)
Total liabilities at fair value | (7,026.4) | (6,614.6)
Fair Value, Recurring | Netting | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | (15.0) | (22.9)
Fair Value, Recurring | Netting | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | (3,227.1) | (2,737.3)
Fair Value, Recurring | Netting | Payable to broker-dealers, clearing organizations and counterparties |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | (3,242.1) | (2,760.2)
Fair Value, Recurring | Netting | Accounts payable and other accrued liabilities - contingent liabilities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Accounts payable and other accrued liabilities |  | 0.0
Fair Value, Recurring | Netting | Physical commodities inventory |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 0.0 | 0.0
Fair Value, Recurring | Netting | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | (593.2) | (375.2)
Financial instruments sold, not yet purchased | (513.2) | (314.3)
Fair Value, Recurring | Netting | Equity securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | Corporate and municipal bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | U.S. government agency obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | Agency mortgage-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | Asset-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Fair Value, Recurring | Netting | Exchange firm common stock |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Fair Value, Recurring | Netting | Cash flow hedges |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | Mutual funds and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Fair Value, Recurring | Netting | Other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments sold, not yet purchased | 0.0 | 0.0
Fair Value, Recurring | Netting | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | (24.7) | (18.3)
Fair Value, Recurring | Netting | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Fair Value, Recurring | Netting | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Fair Value, Recurring | Netting | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | (6,022.8) | (5,740.1)
Fair Value, Recurring | Netting | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 0.0 | 0.0
Fair Value, Recurring | Netting | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 0.0 |
Level 1 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents | 45.8 | 49.2
Securities and other assets segregated under federal and other regulations | 309.0 | 51.8
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 7,965.1 | 6,851.6
Receivables from clients, net - Derivatives | (7.0) | 22.4
Financial instruments owned | 1,237.5 | 1,598.6
Total assets at fair value | 9,751.4 | 8,781.2
Accounts payable and other accrued liabilities | 0.0 |
Payables to clients - Derivatives | 3,401.7 | 3,577.1
Financial instruments sold, not yet purchased | 3,007.6 | 2,408.2
Total liabilities at fair value | 6,688.6 | 6,363.3
Level 1 | Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 0.0 | 0.0
Level 1 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 279.3 | 378.0
Level 1 | Fair Value, Recurring | Payable to broker-dealers, clearing organizations and counterparties |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 279.3 | 378.0
Level 1 | Fair Value, Recurring | Accounts payable and other accrued liabilities - contingent liabilities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Accounts payable and other accrued liabilities |  | 0.0
Level 1 | Fair Value, Recurring | Physical commodities inventory |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 201.0 | 207.6
Level 1 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 623.7 | 1,088.6
Financial instruments sold, not yet purchased | 2,583.2 | 2,139.3
Level 1 | Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.8 | 41.4
Financial instruments sold, not yet purchased | 0.8 | 41.0
Level 1 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.1
Financial instruments sold, not yet purchased | 3.3 | 8.1
Level 1 | Fair Value, Recurring | Equity securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 515.9 | 363.9
Financial instruments sold, not yet purchased | 420.3 | 219.8
Level 1 | Fair Value, Recurring | Corporate and municipal bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 1 | Fair Value, Recurring | U.S. government agency obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 1 | Fair Value, Recurring | Agency mortgage-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 1 | Fair Value, Recurring | Asset-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 1 | Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 61.0 | 67.8
Level 1 | Fair Value, Recurring | Exchange firm common stock |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 13.9 | 13.2
Level 1 | Fair Value, Recurring | Cash flow hedges |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 1 | Fair Value, Recurring | Mutual funds and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 22.2 | 23.6
Level 1 | Fair Value, Recurring | Other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 1 | Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Level 1 | Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 16.7 | 18.3
Level 1 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 4,241.5 | 2,933.2
Level 1 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 3,706.9 | 3,900.1
Level 1 | Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 9.1 | 51.8
Level 1 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 299.9 |
Level 2 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents | 0.0 | 0.0
Securities and other assets segregated under federal and other regulations | 0.0 | 0.0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 2,863.7 | 2,194.3
Receivables from clients, net - Derivatives | 499.5 | 506.2
Financial instruments owned | 6,271.7 | 5,541.6
Total assets at fair value | 9,910.6 | 8,411.1
Accounts payable and other accrued liabilities | 0.0 |
Payables to clients - Derivatives | 240.5 | 228.9
Financial instruments sold, not yet purchased | 1,046.4 | 758.5
Total liabilities at fair value | 4,287.2 | 3,368.2
Level 2 | Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 30.9 | 24.4
Level 2 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 2,969.4 | 2,356.4
Level 2 | Fair Value, Recurring | Payable to broker-dealers, clearing organizations and counterparties |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 3,000.3 | 2,380.8
Level 2 | Fair Value, Recurring | Accounts payable and other accrued liabilities - contingent liabilities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Accounts payable and other accrued liabilities |  | 0.0
Level 2 | Fair Value, Recurring | Physical commodities inventory |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 275.7 | 169.0
Level 2 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 2 | Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 2 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 819.2 | 603.2
Financial instruments sold, not yet purchased | 798.8 | 571.0
Level 2 | Fair Value, Recurring | Equity securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 24.4 | 15.0
Financial instruments sold, not yet purchased | 9.5 | 5.0
Level 2 | Fair Value, Recurring | Corporate and municipal bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 475.6 | 322.1
Financial instruments sold, not yet purchased | 230.3 | 154.6
Level 2 | Fair Value, Recurring | U.S. government agency obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 488.7 | 531.0
Financial instruments sold, not yet purchased | 0.2 | 0.2
Level 2 | Fair Value, Recurring | Agency mortgage-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 4,197.1 | 3,837.2
Financial instruments sold, not yet purchased | 1.7 | 23.6
Level 2 | Fair Value, Recurring | Asset-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 265.5 | 223.5
Financial instruments sold, not yet purchased | 5.0 | 3.9
Level 2 | Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Level 2 | Fair Value, Recurring | Exchange firm common stock |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Level 2 | Fair Value, Recurring | Cash flow hedges |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 1.2 | 9.6
Financial instruments sold, not yet purchased | 0.9 | 0.2
Level 2 | Fair Value, Recurring | Mutual funds and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Level 2 | Fair Value, Recurring | Other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 2 | Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 74.0 | 26.1
Level 2 | Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Level 2 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Level 2 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 2,789.7 | 2,168.2
Level 2 | Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 0.0 | 0.0
Level 2 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 0.0 |
Level 3 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents | 0.0 | 0.0
Securities and other assets segregated under federal and other regulations | 0.0 | 0.0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Receivables from clients, net - Derivatives | 0.0 | 0.0
Financial instruments owned | 2.1 | 2.1
Total assets at fair value | 2.1 | 2.1
Accounts payable and other accrued liabilities | 2.9 |
Payables to clients - Derivatives | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.8 | 0.9
Total liabilities at fair value | 3.7 | 3.2
Level 3 | Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Payable to broker-dealers, clearing organizations and counterparties |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Payable to broker-dealers, clearing organizations and counterparties | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Accounts payable and other accrued liabilities - contingent liabilities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Accounts payable and other accrued liabilities |  | 2.3
Level 3 | Fair Value, Recurring | Physical commodities inventory |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Physical commodities inventory | 0.0 | 0.0
Level 3 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Equity securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Corporate and municipal bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | U.S. government agency obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Agency mortgage-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Asset-backed obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Exchange firm common stock |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Cash flow hedges |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 0.0 | 0.0
Financial instruments sold, not yet purchased | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Mutual funds and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments owned | 2.1 | 2.1
Level 3 | Fair Value, Recurring | Other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments sold, not yet purchased | 0.8 | 0.9
Level 3 | Fair Value, Recurring | To be announced and forward settling securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Foreign government obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Level 3 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Derivatives |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 0.0 | 0.0
Level 3 | Fair Value, Recurring | Commodities warehouse receipts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 0.0 | 0.0
Level 3 | Fair Value, Recurring | U.S. Treasury obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Securities and other assets segregated under federal and other regulations | 0.0 |
Certificates of deposit | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 10.2 | 13.9
Certificates of deposit | Fair Value, Recurring | Netting |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 0.0 | 0.0
Certificates of deposit | Level 1 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 10.2 | 13.9
Certificates of deposit | Level 2 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 0.0 | 0.0
Certificates of deposit | Level 3 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 0.0 | 0.0
Money market mutual funds | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 35.6 | 35.3
Money market mutual funds | Fair Value, Recurring | Netting |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 0.0 | 0.0
Money market mutual funds | Level 1 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 35.6 | 35.3
Money market mutual funds | Level 2 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | 0.0 | 0.0
Money market mutual funds | Level 3 | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets | $ 0.0 | $ 0.0

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