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	Sep. 30, 2019	Dec. 31, 2018
Reverse repurchase agreements
Gross Amounts of Recognized Assets	$ 91,473	$ 82,429
Gross Amounts Offset on the Balance Sheet	(91,473)	(82,139)
Net Amounts of Assets Presented on the Balance Sheet	0	290
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	0	290
Securities borrowed
Gross Amounts of Recognized Assets	103,738	108,144
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Assets Presented on the Balance Sheet	103,738	108,144
Financial Instruments	(100,188)	(105,960)
Cash Collateral Received	0	0
Net Amount	3,550	2,184
Total
Gross Amounts of Recognized Assets	195,211	190,573
Gross Amounts Offset on the Balance Sheet	(91,473)	(82,139)
Net Amounts of Assets Presented on the Balance Sheet	103,738	108,434
Financial Instruments	(100,188)	(105,960)
Cash Collateral Received	0	0
Net Amount	3,550	2,474
Repurchase agreements
Gross Amounts of Recognized Liabilities	345,193	566,357
Gross Amounts Offset on the Balance Sheet	(91,473)	(82,139)
Net Amounts of Liabilities Presented on the Balance Sheet	253,720	484,218
Financial Instruments	(252,401)	(480,322)
Cash Collateral Pledged	0	0
Net Amount	1,319	3,896
Securities loaned
Gross Amounts of Recognized Liabilities	209,298	146,815
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Liabilities Presented on the Balance Sheet	209,298	146,815
Financial Instruments	(203,747)	(139,232)
Cash Collateral Pledged	0	0
Net Amount	5,551	7,583
Total
Gross Amounts of Recognized Liabilities	554,491	713,172
Gross Amounts Offset on the Balance Sheet	(91,473)	(82,139)
Net Amounts of Liabilities Presented on the Balance Sheet	463,018	631,033
Financial Instruments	(456,148)	(619,554)
Cash Collateral Pledged	0	0
Net Amount	$ 6,870	$ 11,479