Receivables from/Payables to Broker-Dealers and Clearing Organizations (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets
Due from prime brokers	$ 129,273	$ 101,372
Deposits with clearing organizations	32,968	31,908
Net equity with futures commission merchants	157,900	174,615
Unsettled trades with clearing organization	76,301	102,890
Securities failed to deliver	116,850	65,751
Total receivables from broker-dealers and clearing organizations	513,292	476,536
Liabilities
Due to prime brokers	285,189	294,691
Net equity with futures commission merchants		46,537
Unsettled trades with clearing organization	20,067	145,376
Total payables to broker-dealers and clearing organizations	305,256	486,604
Outstanding principal balance	$ 253,200	$ 219,100