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, 2019	Dec. 31, 2018
Reverse repurchase agreements
Gross Amounts of Recognized Assets	$ 101,077	$ 82,429
Gross Amounts Offset on the Balance Sheet	(100,488)	(82,139)
Net Amounts of Assets Presented on the Balance Sheet	589	290
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	589	290
Securities borrowed
Gross Amounts of Recognized Assets	109,712	108,144
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Assets Presented on the Balance Sheet	109,712	108,144
Financial Instruments	(107,985)	(105,960)
Cash Collateral Received	0	0
Net Amount	1,727	2,184
Total
Gross Amounts of Recognized Assets	210,789	190,573
Gross Amounts Offset on the Balance Sheet	(100,488)	(82,139)
Net Amounts of Assets Presented on the Balance Sheet	110,301	108,434
Financial Instruments	(107,985)	(105,960)
Cash Collateral Received	0	0
Net Amount	2,316	2,474
Repurchase agreements
Gross Amounts of Recognized Liabilities	369,109	566,357
Gross Amounts Offset on the Balance Sheet	(100,488)	(82,139)
Net Amounts of Liabilities Presented on the Balance Sheet	268,621	484,218
Financial Instruments	(268,156)	(480,322)
Cash Collateral Pledged	0	0
Net Amount	465	3,896
Securities loaned
Gross Amounts of Recognized Liabilities	232,370	146,815
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Liabilities Presented on the Balance Sheet	232,370	146,815
Financial Instruments	(225,992)	(139,232)
Cash Collateral Pledged	0	0
Net Amount	6,378	7,583
Total
Gross Amounts of Recognized Liabilities	601,479	713,172
Gross Amounts Offset on the Balance Sheet	(100,488)	(82,139)
Net Amounts of Liabilities Presented on the Balance Sheet	500,991	631,033
Financial Instruments	(494,148)	(619,554)
Cash Collateral Pledged	0	0
Net Amount	$ 6,843	$ 11,479