Receivables from/Payables to Broker-Dealers and Clearing Organizations (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Assets
Due from prime brokers	$ 200,286	$ 101,372
Deposits with clearing organizations	46,584	31,908
Net equity with futures commission merchants	171,383	174,615
Unsettled trades with clearing organization	876,587	102,890
Securities failed to deliver	54,524	65,751
Total receivables from broker-dealers and clearing organizations	1,349,364	476,536
Liabilities
Due to prime brokers	273,565	294,691
Net equity with futures commission merchants	39,519	46,537
Unsettled trades with clearing organization	94,698	145,376
Securities failed to receive	281
Total payables to broker-dealers and clearing organizations	408,063	486,604
Outstanding principal balance	$ 265,700	$ 219,100