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Amount of receivables arising from transactions with related parties due within one year or the normal operating cycle, if longer.

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Amount of unrealized and realized gain (loss) on investment in debt and equity securities.

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Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

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The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

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Fair value of obligations incurred from short sales.

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Amount payable to broker-dealers and clearing organizations, including, but not limited to, securities failed-to-receive, certain deposits received for securities loaned, open transactions, and floor-brokerage payables.

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The cash outflow associated with the purchase of all investments (debt, security, other) during the period.

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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Related Party Transactions - Jefferies (Detail)				1 Months Ended				3 Months Ended		9 Months Ended
Related Party Transactions - Jefferies (Detail)	Sep. 25, 2018 USD ($)	Jun. 15, 2018 USD ($)	Apr. 03, 2018 USD ($)	Jan. 31, 2018 USD ($)	Aug. 31, 2017 USD ($)	Apr. 30, 2017 USD ($)	Feb. 28, 2017 USD ($)	Aug. 31, 2018 USD ($) Warrant Public_Offering_Unit shares	Aug. 31, 2017 USD ($)	Aug. 31, 2018 USD ($) Warrant Public_Offering_Unit shares	Aug. 31, 2017 USD ($)	Nov. 30, 2017 USD ($) Warrant Public_Offering_Unit shares
Related Party Transaction [Line Items]
Payments of dividends										$ 218,593,000	$ 0
Payables-brokers, dealers and clearing organizations								$ 1,938,308,000		1,938,308,000		$ 2,226,768,000
Financial instruments sold, not yet purchased								8,128,200,000		8,128,200,000		8,171,929,000
Financial instruments owned, at fair value								15,195,619,000		15,195,619,000		14,193,352,000
Jefferies \| Accrued expenses and other liabilities
Related Party Transaction [Line Items]
Tax payable								44,000,000		44,000,000		91,500,000
Payment made to related party related to tax sharing agreement		$ 36,000,000	$ 115,000,000
Jefferies \| Affiliated Entity
Related Party Transaction [Line Items]
Charges to Jefferies for services provided								15,800,000	$ 13,000,000	46,100,000	34,800,000
Charges from Jefferies for services received								2,200,000	4,900,000	6,900,000	13,800,000
Receivable from Jefferies								3,200,000		3,200,000		2,500,000
Payable to Jefferies				$ 200,000,000				600,000		$ 600,000		3,100,000
Quarterly dividend as percentage of net earnings										50.00%
Payments of dividends								18,600,000
Dividends payable								30,100,000		$ 30,100,000
Payments to acquire investments				$ 26,700,000
Gain (loss) on sale of securities										0
Proceeds from sale of securities					$ 7,100,000	$ 21,900,000	$ 25,600,000
Jefferies \| Affiliated Entity \| Investment banking
Related Party Transaction [Line Items]
Charges to Jefferies for services provided								5,600,000	0	5,600,000	0
Jefferies \| Affiliated Entity \| Commissions and other fees
Related Party Transaction [Line Items]
Charges to Jefferies for services provided								100,000	0	500,000	0
Jefferies \| Affiliated Entity \| Principal transactions
Related Party Transaction [Line Items]
Charges to Jefferies for services provided								0	0	100,000	0
Jefferies \| Affiliated Entity \| Other revenues
Related Party Transaction [Line Items]
Charges to Jefferies for services provided								300,000	0	700,000	0
Affiliate of Jefferies \| Affiliated Entity
Related Party Transaction [Line Items]
Payables-brokers, dealers and clearing organizations								12,300,000		12,300,000		17,000,000
Hedge Fund Managed By Jefferies \| Affiliated Entity
Related Party Transaction [Line Items]
Investment in related party								218,100,000		218,100,000		$ 136,100,000
Net gain on investment in hedge fund								$ 500,000	$ 1,900,000	$ 5,000,000	$ 5,100,000
Landcadia Holdings Inc. \| Affiliated Entity
Related Party Transaction [Line Items]
Number of public offering units owned \| Public_Offering_Unit								638,561		638,561		638,561
Number of common stock per public offering unit (in shares) \| shares								1		1		1
Number of public warrant per public offering unit \| Warrant								1		1		1
Financial instruments owned, at fair value								$ 7,100,000		$ 7,100,000		$ 6,800,000
Corporate debt securities \| Jefferies \| Affiliated Entity
Related Party Transaction [Line Items]
Financial instruments owned, at fair value								1,500,000		1,500,000		200,000
Director \| Affiliated Entity
Related Party Transaction [Line Items]
Investment in related party								4,800,000		4,800,000		4,900,000
Director \| Hedge Fund Managed By Jefferies \| Affiliated Entity
Related Party Transaction [Line Items]
Investment in related party								$ 2,800,000		$ 2,800,000		3,600,000
Subsequent Event \| Jefferies \| Accrued expenses and other liabilities
Related Party Transaction [Line Items]
Payment made to related party related to tax sharing agreement	$ 42,000,000
Subsidiary Of Jefferies
Related Party Transaction [Line Items]
Investment in related party												$ 27,300,000