Collateralized Transactions - Schedule of Gross Amounts and Offsetting Amounts of Reverse Repurchase Agreements, Repurchase Agreements, Securities Borrowed and Securities Lending Transactions (Details) - USD ($) $ in Thousands	Dec. 31, 2016		Dec. 31, 2015
Reverse repurchase agreements
Gross Amounts of Recognized Assets	$ 24,006		$ 282,042
Gross Amounts Offset on the Balance Sheet	0		(75,543)
Net Amounts of Assets Presented on the Balance Sheet	24,006		206,499
Financial Instruments	(23,972)		(203,266)
Cash Collateral Received	0		0
Net Amount	34		3,233
Securities borrowed
Gross Amounts of Recognized Assets	154,090	[1]	224,672	[2]
Gross Amounts Offset on the Balance Sheet	0	[1]	0	[2]
Net Amounts of Assets Presented on the Balance Sheet	154,090	[1]	224,672	[2]
Financial Instruments	(150,510)	[1]	(219,099)	[2]
Cash Collateral Received	0	[1]	0	[2]
Net Amount	3,580	[1]	5,573	[2]
Total
Gross Amounts of Recognized Assets	178,096		506,714
Gross Amounts Offset on the Balance Sheet	0		(75,543)
Net Amounts of Assets Presented on the Balance Sheet	178,096		431,171
Financial Instruments	(174,482)		(422,365)
Cash Collateral Received	0		0
Net Amount	3,614		8,806
Repurchase agreements
Gross Amounts of Recognized Liabilities	378,084		726,988
Gross Amounts Offset on the Balance Sheet	0		(75,543)
Net Amounts of Liabilities Presented on the Balance Sheet	378,084		651,445
Financial Instruments	(376,273)		(645,498)
Cash Collateral Pledged	0		0
Net Amount	1,811		5,947
Securities loaned
Gross Amounts of Recognized Liabilities	179,875	[3]	130,658	[4]
Gross Amounts Offset on the Balance Sheet	0	[3]	0	[4]
Net Amounts of Liabilities Presented on the Balance Sheet	179,875	[3]	130,658	[4]
Financial Instruments	(171,991)	[3]	(122,650)	[4]
Cash Collateral Pledged	0	[3]	0	[4]
Net Amount	7,884	[3]	8,008	[4]
Total
Gross Amounts of Recognized Liabilities	557,959		857,646
Gross Amounts Offset on the Balance Sheet	0		(75,543)
Net Amounts of Liabilities Presented on the Balance Sheet	557,959		782,103
Financial Instruments	(548,264)		(768,148)
Cash Collateral Pledged	0		0
Net Amount	$ 9,695		$ 13,955

[1] Included in receivable from brokers, dealers and clearing organizations on the consolidated balance sheet.

[2] Included in receivable from brokers, dealers and clearing organizations on the consolidated balance sheet.

[3] Included in payable to brokers, dealers and clearing organizations on the consolidated balance sheet.

[4] Included in payable to brokers, dealers and clearing organizations on the consolidated balance sheet.