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, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase, Gross	$ 619,615	$ 750,100
Securities Purchased under Agreements to Resell, Gross	222,226	314,266
Securities Purchased under Agreements to Resell, Liability	222,226	62,660
Net Amounts of Assets Presented on the Balance Sheet	0	251,606
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Securities	0	(250,000)
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Cash	0	0
Securities Purchased under Agreements to Resell, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	0	1,606
Net Amounts of Liabilities Presented on the Balance Sheet	397,389	687,440
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	(395,376)	(686,119)
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash	0	0
Securities Sold under Agreements to Repurchase, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	2,013	1,321
Securities Loaned, Gross	165,005	137,892
Securities Loaned, Asset	0	0
Gross Amounts of Recognized Assets	488,789	556,438
Gross Amounts Offset in the Balance Sheet	(222,226)	(62,660)
Net Amounts of Assets Presented on the Balance Sheet	266,563	493,778
Financial Instruments	(256,386)	(484,376)
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Cash	0	0
Net Amount	10,177	9,402
Securities Borrowed, Gross	266,563	242,172
Securities Borrowed, Liability	0	0
Securities borrowed	266,563	242,172
Securities Borrowed, Collateral, Obligation to Return Cash	0	0
Securities Borrowed, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	10,177	7,796
Gross Amounts of Recognized Liabilities	784,620	887,992
Securities loaned	165,005	137,892
Securities Loaned, Collateral, Right to Reclaim Securities	(158,125)	(132,258)
Securities Loaned, Collateral, Right to Reclaim Cash	0	0
Securities Loaned, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	6,880	5,634
Gross Amounts Offset in the Balance Sheet	(222,226)	(62,660)
Net Amounts of Liabilities Presented on the Balance Sheet	562,394	825,332
Financial Instruments	(553,501)	(818,377)
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Cash	0	0
Net Amount	8,893	6,955
Securities Borrowed [Member]
Securities Financing Transaction [Line Items]
Securities Borrowed, Collateral, Obligation to Return Securities	(256,386)	(234,376)
Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase, Asset	$ 222,226	$ 62,660