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		Dec. 31, 2019		Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities Owned And Pledged As Collateral Amount Not Eligible To Be Repledged By Counterparty Carrying Value		$ 0		$ 20,200
Reverse repurchase agreements
Gross Amounts of Recognized Assets		55,927		82,429
Gross Amounts Offset on the Balance Sheet		(55,927)		(82,139)
Securities Purchased under Agreement to Resell, Amount Not Offset Against Collateral				290
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		99,635	[1]	108,144	[2]
Gross Amounts Offset on the Balance Sheet		0	[1]	0	[2]
Securities Borrowed, Amount Not Offset Against Collateral	[2]			108,144
Net Amounts of Assets Presented on the Balance Sheet		99,635		108,144
Financial Instruments		(97,702)	[1]	(105,960)	[2]
Cash Collateral Received		0	[1]	0	[2]
Net Amount		1,933	[1]	2,184	[2]
Total
Gross Amounts of Recognized Assets		155,562		190,573
Gross Amounts Offset on the Balance Sheet		(55,927)		(82,139)
Net Amounts of Assets Presented on the Balance Sheet		99,635		108,434
Financial Instruments		(97,702)		(105,960)
Cash Collateral Received		0		0
Net Amount		1,933		2,474
Repurchase agreements
Gross Amounts of Recognized Liabilities				566,357
Gross Amounts Offset on the Balance Sheet		(55,927)		(82,139)
Securities Sold under Agreements to Repurchase, Amount Not Offset Against Collateral				484,218
Net Amounts of Liabilities Presented on the Balance Sheet		287,265		484,218
Financial Instruments		(285,264)		(480,322)
Cash Collateral Pledged		0		0
Net Amount		2,001		3,896
Securities loaned
Gross Amounts of Recognized Liabilities	[3]			146,815
Gross Amounts Offset on the Balance Sheet		0	[4]	0	[3]
Securities Loaned, Amount Not Offset Against Collateral	[3]			146,815
Net Amounts of Liabilities Presented on the Balance Sheet		234,343		146,815
Financial Instruments		(228,548)	[4]	(139,232)	[3]
Cash Collateral Pledged		0	[4]	0	[3]
Net Amount		5,795	[4]	7,583	[3]
Total
Gross Amounts of Recognized Liabilities		577,535		713,172
Gross Amounts Offset on the Balance Sheet		(55,927)		(82,139)
Net Amounts of Liabilities Presented on the Balance Sheet		521,608		631,033
Financial Instruments		(513,812)		(619,554)
Cash Collateral Pledged		0		0
Net Amount		7,796		$ 11,479
U.S. treasury, agency and sovereign obligations | Maturity Overnight and on Demand [Member]
Repurchase agreements
Gross Amounts of Recognized Liabilities		343,192
Equity Securities [Member] | Maturity Overnight and on Demand [Member]
Securities loaned
Gross Amounts of Recognized Liabilities	[4]	$ 234,343

[1] (1) Included in receivable from brokers, dealers and clearing organizations on the consolidated balance sheet. Gross Amounts Not Offseton the Balance Sheet GrossAmounts ofRecognizedLiabilities GrossAmountsOffset on the Balance Sheet Net Amountsof LiabilitiesPresented onthe Balance Sheet FinancialInstruments CashCollateralPledged Net AmountRepurchase agreements$343,192 $(55,927) $287,265 $(285,264) $— $2,001Securities loaned (2)234,343 — 234,343 (228,548) — 5,795Total$577,535 $(55,927) $521,608 $(513,812) $— $7,796 (2) Included in payable to brokers, dealers and clearing organizations on the consolidated balance she

[2] (1) Included in receivable from brokers, dealers and clearing organizations on the consolidated balance sheet. Gross Amounts Not Offseton the Balance Sheet GrossAmounts ofRecognizedLiabilities GrossAmountsOffset on the Balance Sheet Net Amountsof LiabilitiesPresented onthe Balance Sheet FinancialInstruments CashCollateralPledged Net AmountRepurchase agreements$566,357 $(82,139) $484,218 $(480,322) $— $3,896Securities loaned (2)146,815 — 146,815 (139,232) — 7,583Total$713,172 $(82,139) $631,033 $(619,554) $— $11,479

[3] (2) Included in payable to brokers, dealers and clearing organizations on the consolidated balance sheet.

[4] As of December 31, 2018(Expressed in thousands) Gross Amounts Not Offseton the Balance Sheet GrossAmounts ofRecognizedAssets GrossAmountsOffset on the Balance Sheet Net Amountsof AssetsPresented onthe Balance Sheet FinancialInstruments CashCollateralReceived Net AmountReverse repurchase agreements$82,429 $(82,139) $290 $— $— $290Securities borrowed (1)108,144 — 108,144 (105,960) — 2,184Total$190,573 $(82,139) $108,434 $(105,960) $— $2,474