Collateralized Transactions - Gross Amounts Offset (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets, Securities Borrowed
Gross Amounts Recognized	$ 1,636,284	$ 1,632,062
Gross Amounts Offset in the Statements of Financial Condition	0	0
Net Amounts Presented in the Statements of Financial Condition	1,636,284	1,632,062
Gross Amounts Not Offset in the Statement of Financial Condition, Available Collateral	1,575,568	1,570,194
Gross Amounts Not Offset in the Statement of Financial Condition, Counterparty Netting	8,277	15,782
Net Amount	52,439	46,086
Assets, Receivable from Brokers, Dealers and Clearing Organizations
Gross Amounts Recognized	65,433	21,545
Gross Amounts Offset in the Statements of Financial Condition	0	0
Net Amounts Presented in the Statements of Financial Condition	65,433	21,545
Gross Amounts Not Offset in the Statement of Financial Condition, Available Collateral	62,580	21,425
Gross Amounts Not Offset in the Statement of Financial Condition, Counterparty Netting	0	0
Net Amount	2,853	120
Total Assets
Gross Amounts Recognized	1,701,717	1,653,607
Gross Amounts Offset in the Statements of Financial Condition	0	0
Net Amounts Presented in the Statements of Financial Condition	1,701,717	1,653,607
Gross Amounts Not Offset in the Statement of Financial Condition, Available Collateral	1,638,148	1,591,619
Gross Amounts Not Offset in the Statement of Financial Condition, Counterparty Netting	8,277	15,782
Net Amount	55,292	46,206
Liabilities, Securities Loaned
Gross Amounts Recognized	463,377	707,744
Gross Amounts Offset in the Statements of Financial Condition	0	0
Net Amounts Presented in the Statements of Financial Condition	463,377	707,744
Gross Amounts Not Offset in the Statement of Financial Condition, Available Collateral	440,486	682,389
Gross Amounts Not Offset in the Statement of Financial Condition, Counterparty Netting	8,277	15,782
Net Amount	14,614	9,573
Liabilities, Financial Instruments Sold Under Agreements to Repurchase
Gross Amounts Recognized	954,902	933,576
Gross Amounts Offset in the Statements of Financial Condition	0	0
Net Amounts Presented in the Statements of Financial Condition	954,902	933,576
Gross Amounts Not Offset in the Statement of Financial Condition, Available Collateral	954,902	933,560
Gross Amounts Not Offset in the Statement of Financial Condition, Counterparty Netting	0	0
Net Amount	0	16
Total Liabilities
Gross Amounts Recognized	1,418,279	1,641,320
Gross Amounts Offset in the Statements of Financial Condition	0	0
Net Amounts Presented in the Statements of Financial Condition	1,418,279	1,641,320
Gross Amounts Not Offset in the Statement of Financial Condition, Available Collateral	1,395,388	1,615,949
Gross Amounts Not Offset in the Statement of Financial Condition, Counterparty Netting	8,277	15,782
Net Amount	$ 14,614	$ 9,589