Receivables from and Payables to Broker-dealers, Clearing Organizations and Customers - Schedule of Receivables from and Payables to Broker-dealers, Clearing Organizations and Customers (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Receivables from broker-dealers, clearing organizations and customers:
Securities failed-to-deliver - broker-dealers	$ 131,125	$ 93,294
Securities failed-to-deliver - customers	259,790	87,685
Deposits with clearing organizations and broker-dealers	81,433	97,043
Other	3,391	1,893
Total	475,739	279,915
Payables to broker-dealers, clearing organizations and customers:
Securities failed-to-receive - broker-dealers	202,794	70,917
Securities failed-to-receive - customers	72,069	60,784
Other	3,440	1,625
Total	$ 278,303	$ 133,326