Related Party Transactions - Other Transactions (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2022	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Feb. 15, 2022	Feb. 25, 2021
Related Party Transaction [Line Items]
Receivables from related parties		$ 5,458,000		$ 5,458,000		$ 2,717,000
Related Party
Related Party Transaction [Line Items]
Interest income		4,400,000	$ 2,000,000.0	10,200,000	$ 5,900,000
Due from related parties, write-offs							$ 600,000
Receivables from related parties						$ 400,000
Related Party | Subordinated Loan Agreement with Aqua
Related Party Transaction [Line Items]
Interest income	$ 0
Aqua | Cantor | Related Party
Related Party Transaction [Line Items]
Investment ownership percentage									51.00%
Aqua | Related Party
Related Party Transaction [Line Items]
Increase in authorization amount for loans and investments, other credit support arrangements								$ 1,000,000.0	$ 1,000,000.0
Authorization amount for loans and investments, other credit support arrangements									$ 21,200,000
Aqua | Related Party | Subordinated Loan Agreement with Aqua
Related Party Transaction [Line Items]
Receivables from related parties		$ 1,000,000.0		$ 1,000,000.0
Aqua | Aqua | BGC Partners, Inc. | Related Party
Related Party Transaction [Line Items]
Percentage of ownership interest									49.00%