Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Receivable:
Clearing organizations and other	$ 619,425	$ 505,789
Financial instruments purchased under agreement to resell	21,832	65,433
Securities failed to deliver	191,528	109,989
Total receivable	832,785	681,211
Payable:
Clearing organizations and other	458,341	240,985
Securities failed to receive	60,559	32,820
Total payable	$ 518,900	$ 273,805