Related Party Transactions - Other Transactions (Details) - USD ($)		1 Months Ended	3 Months Ended		6 Months Ended
	Oct. 25, 2016	Nov. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Feb. 25, 2021	Feb. 25, 2020	Nov. 04, 2016
Related Party Transaction [Line Items]
Equity investment					$ 0	$ 466,000
Related Party
Related Party Transaction [Line Items]
Interest income			$ 2,100,000	$ 2,300,000	3,900,000	3,500,000
Due from related parties, write-offs							$ 600,000
Due from related parties, remaining amount receivable			400,000		400,000
Related Party | Transactions with Newmark
Related Party Transaction [Line Items]
Payables to related parties			$ 0		$ 0			$ 8,300,000
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%		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	$ 1,000,000
Authorization amount for loans and investments, other credit support arrangements									$ 21,200,000
Equity investment			$ 0	$ 100,000	$ 0	$ 500,000
Aqua | Related Party | Subordinated Loan Agreement with Aqua
Related Party Transaction [Line Items]
Receivables from related parties			$ 1,000,000		$ 1,000,000
Aqua | Aqua | BGC Partners, Inc. | Related Party
Related Party Transaction [Line Items]
Percentage of ownership interest			49.00%		49.00%
Lucera | Related Party | Class B Units
Related Party Transaction [Line Items]
Purchase of units (in shares)	9,000
Percentage of outstanding common stock owned by parent											100.00%