Related Party Transactions - Receivables from and Payables to Related Broker-Dealers (Details) - Related Party - USD ($)	Jun. 30, 2024	Dec. 31, 2023
Transactions with Freedom
Related Party Transaction [Line Items]
Receivables from related parties	$ 2,100,000	$ 1,400,000
Open Derivative Contracts with Cantor
Related Party Transaction [Line Items]
Receivables from related parties	3,900,000	2,700,000
Payables to related parties	1,200,000	4,900,000
Fails and Pending Trades with Cantor
Related Party Transaction [Line Items]
Payables to related parties	$ 9,300,000	$ 800,000