Divestiture - Schedule of Assets and Liabilities Included in Sale of Business (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Apr. 01, 2024	Mar. 31, 2024	Dec. 31, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assets sold	$ 0			$ 564,776
Total liabilities sold	$ 0			153,342
Disposal Group, Held-for-Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents			$ 69,100	153,047
Investments				17,029
Furniture and equipment, net				5,807
Other assets				104,228
Right-of-use assets				5,032
Intangible assets				4,061
Goodwill				159,826
Valuation adjustment (allowance) on disposal group				(6,600)
Total assets sold				564,776
Brokers and dealers				39,359
Brokerage clients				16,885
Other liabilities				67,938
Accrued compensation and benefits				29,160
Total liabilities sold				153,342
Disposal Group, Held-for-Sale, Not Discontinued Operations | Brokers and dealers
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Receivables, net:				32,669
Disposal Group, Held-for-Sale, Not Discontinued Operations | Brokerage clients
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Receivables, net:				74,351
Disposal Group, Held-for-Sale, Not Discontinued Operations | Other fees
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Receivables, net:				$ 15,326
Investment in joint ventures | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents		$ 338,226
Investments		9,555
Furniture and equipment, net		5,472
Other assets		44,751
Right-of-use assets		4,422
Intangible assets		3,850
Goodwill		159,826
Total assets sold		615,065
Brokers and dealers		15,271
Brokerage clients		14,110
AP and Accrued Expenses		134,979
Other liabilities		10,370
Accrued compensation and benefits		42,069
Debt		86,200
Total liabilities sold		302,999
Net carrying amount of assets and liabilities divested		312,066
Investment in joint ventures | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Brokers and dealers
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Receivables, net:		31,427
Investment in joint ventures | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Brokerage clients
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Receivables, net:		2,817
Investment in joint ventures | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Other fees
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Receivables, net:		$ 14,719