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	Mar. 31, 2016	Dec. 31, 2015
Reverse repurchase agreements
Securities Purchased under Agreements to Resell, Gross	$ 320,688	$ 282,042
Securities Purchased under Agreements to Resell, Liability	320,688	75,543
Securities purchased under agreements to resell	0	206,499
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Securities	0	(203,266)
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	3,233
Securities borrowed
Securities Borrowed, Gross	190,963	224,672
Securities Borrowed, Liability	0	0
Securities borrowed	190,963	224,672
Securities Borrowed, Collateral, Obligation to Return Securities	(185,319)
Securities Borrowed, Collateral, Obligation to Return Cash	0	0
Securities Borrowed, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	5,644	5,573
Gross Amounts of Recognized Assets	511,651	506,714
Gross Amounts Offset in the Balance Sheet	(320,688)	(75,543)
Net Amounts of Assets Presented on the Balance Sheet	190,963	431,171
Financial Instruments	(185,319)	(422,365)
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Cash	0	0
Net Amount	5,644	8,806
Repurchase agreements
U.S. Treasury and agency securities	850,440	726,988
Securities Sold under Agreements to Repurchase, Asset	320,688
Net Amounts of Liabilities Presented on the Balance Sheet	529,752	651,445
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	(518,518)	(645,498)
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	11,234	5,947
Securities loaned:
Equity securities	143,157	130,658
Securities Loaned, Asset	0	0
Securities loaned	143,157	130,658
Securities Loaned, Collateral, Right to Reclaim Securities	(139,315)	(122,650)
Securities Loaned, Collateral, Right to Reclaim Cash	0	0
Securities Loaned, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	3,842	8,008
Gross amount of recognized liabilities for repurchase agreements and securities loaned	993,597	857,646
Gross Amounts Offset in the Balance Sheet	(320,688)	(75,543)
Net Amounts of Liabilities Presented on the Balance Sheet	672,909	782,103
Financial Instruments	(657,833)	(768,148)
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Cash	0	0
Net Amount	$ 15,076	13,955
Securities Borrowed [Member]
Securities borrowed
Securities Borrowed, Collateral, Obligation to Return Securities		(219,099)
Repurchase Agreements [Member]
Repurchase agreements
Securities Sold under Agreements to Repurchase, Asset		$ 75,543