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	Jun. 30, 2019	Dec. 31, 2018
Reverse repurchase agreements
Gross Amounts of Recognized Assets	$ 168,124	$ 82,429
Gross Amounts Offset on the Balance Sheet	(168,085)	(82,139)
Net Amounts of Assets Presented on the Balance Sheet	39	290
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	39	290
Securities borrowed
Gross Amounts of Recognized Assets	103,148	108,144
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Assets Presented on the Balance Sheet	103,148	108,144
Financial Instruments	(100,192)	(105,960)
Cash Collateral Received	0	0
Net Amount	2,956	2,184
Total
Gross Amounts of Recognized Assets	271,272	190,573
Gross Amounts Offset on the Balance Sheet	(168,085)	(82,139)
Net Amounts of Assets Presented on the Balance Sheet	103,187	108,434
Financial Instruments	(100,192)	(105,960)
Cash Collateral Received	0	0
Net Amount	2,995	2,474
Repurchase agreements
Gross Amounts of Recognized Liabilities	689,922	566,357
Gross Amounts Offset on the Balance Sheet	(168,085)	(82,139)
Net Amounts of Liabilities Presented on the Balance Sheet	521,837	484,218
Financial Instruments	(521,022)	(480,322)
Cash Collateral Pledged	0	0
Net Amount	815	3,896
Securities loaned
Gross Amounts of Recognized Liabilities	247,714	146,815
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Liabilities Presented on the Balance Sheet	247,714	146,815
Financial Instruments	(239,713)	(139,232)
Cash Collateral Pledged	0	0
Net Amount	8,001	7,583
Total
Gross Amounts of Recognized Liabilities	937,636	713,172
Gross Amounts Offset on the Balance Sheet	(168,085)	(82,139)
Net Amounts of Liabilities Presented on the Balance Sheet	769,551	631,033
Financial Instruments	(760,735)	(619,554)
Cash Collateral Pledged	0	0
Net Amount	$ 8,816	$ 11,479