Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Receivable:
Clearing organizations and other	$ 575,544	$ 619,425
Financial instruments purchased under agreement to resell	13,735	21,832
Securities failed to deliver	212,399	191,528
Total receivable	801,678	832,785
Payable:
Clearing organizations and other	433,164	458,341
Securities failed to receive	62,089	60,559
Total payable	$ 495,253	$ 518,900