Receivables from and Payables to Brokers, Dealers and Clearing Organizations - Schedule of Receivables from and Payables to Brokers, Dealers and Clearing Organizations (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Receivables from Brokers-Dealers and Clearing Organizations [Abstract]
Receivable from clearing organizations	$ 7,406	$ 260,436
Receivable from brokers and dealers	5,967	19,161
Other	3,589	3,511
Total receivables from brokers, dealers and clearing organizations	16,962	283,108
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization [Abstract]
Payable to brokers and dealers	15,469	7,514
Payable to clearing organizations	732	0
Total payables to brokers, dealers and clearing organizations	$ 16,201	$ 7,514