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) $ in Thousands	Dec. 31, 2020 USD ($)
Receivables from broker-dealers, clearing organizations and customers:
Securities failed-to-deliver - broker-dealers	$ 93,294
Securities failed-to-deliver - customers	87,685
Deposits with clearing organizations and broker-dealers	97,043
Other	1,893
Total	279,915
Payables to broker-dealers, clearing organizations and customers:
Securities failed-to-receive - broker-dealers	70,917
Securities failed-to-receive - customers	60,784
Other	1,625
Total	$ 133,326