Related Party Transactions - Additional Information (Detail)	1 Months Ended							3 Months Ended		7 Months Ended	9 Months Ended
	Aug. 31, 2017 USD ($) Public_Offering_Unit Warrant shares	Jun. 30, 2017 USD ($)	Apr. 30, 2017 USD ($)	Feb. 28, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jul. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Aug. 31, 2017 USD ($) Public_Offering_Unit Warrant shares	Aug. 31, 2016 USD ($)	Aug. 31, 2017 USD ($) Public_Offering_Unit Warrant shares	Aug. 31, 2017 USD ($) Public_Offering_Unit Warrant shares	Aug. 31, 2016 USD ($)	Nov. 30, 2016 USD ($) Public_Offering_Unit Warrant shares
Related Party Transaction [Line Items]
Purchase commitments from Berkadia Commercial Mortgage, LLC	$ 722,900,000							$ 722,900,000		$ 722,900,000	$ 722,900,000		$ 817,000,000.0
Loans outstanding to certain employees	49,300,000							49,300,000		49,300,000	49,300,000		38,400,000
Financial instruments, owned, at fair value	14,036,679,000							14,036,679,000		14,036,679,000	14,036,679,000		13,809,512,000
Financial instruments sold, not yet purchased, at fair value	8,460,500,000							8,460,500,000		8,460,500,000	8,460,500,000		8,359,202,000
Equity Method Investee | Equity Investments in Jefferies Capital Partners Related Funds
Related Party Transaction [Line Items]
Equity investments loans in related funds	28,100,000							28,100,000		28,100,000	28,100,000		37,700,000
Affiliated Entity | Investment Banking and Advisory
Related Party Transaction [Line Items]
Charges to Leucadia for services provided												$ 1,800,000
Leucadia | Accrued expenses and other liabilities
Related Party Transaction [Line Items]
Tax payable	18,000,000.0							18,000,000.0		18,000,000.0	18,000,000.0
Leucadia | Other Assets
Related Party Transaction [Line Items]
Tax receivable													80,100,000
Leucadia | Affiliated Entity
Related Party Transaction [Line Items]
Charges to Leucadia for services provided								13,000,000.0	$ 8,700,000		34,800,000	28,800,000
Charges from Leucadia for services received								4,900,000	3,600,000		13,800,000	9,200,000
Receivable from Leucadia	1,900,000							1,900,000		1,900,000	1,900,000		2,800,000
Payable to Leucadia	2,000,000.0							2,000,000.0		2,000,000.0	2,000,000.0		$ 1,900,000
Proceeds from sale of securities	$ 7,100,000		$ 21,900,000	$ 25,600,000
Gain (loss) on sale of securities										$ 0
Hedge fund Managed by Leucadia | Affiliated Entity
Related Party Transaction [Line Items]
Capital contribution		$ 500,000					$ 114,000,000.0
Capital redemption					$ 17,000,000.0
Net gain on investment in hedge fund								$ 1,900,000	$ 1,500,000		$ 5,100,000	$ 2,400,000
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	638,561		638,561
Number of common stock per public offering unit (in shares) | shares	1							1		1	1		1
Number of public warrant per public offering unit | Warrant	1							1		1	1		1
Financial instruments, owned, at fair value	$ 6,900,000							$ 6,900,000		$ 6,900,000	$ 6,900,000		$ 6,600,000
Subsidy of Leucadia | Affiliated Entity
Related Party Transaction [Line Items]
Capital contribution						$ 30,000,000.0
Corporate debt securities | Leucadia | Affiliated Entity
Related Party Transaction [Line Items]
Financial instruments, owned, at fair value	2,100,000							2,100,000		2,100,000	2,100,000		1,000,000.0
Financial instruments sold, not yet purchased, at fair value	1,100,000							1,100,000		1,100,000	1,100,000
Director | Affiliated Entity
Related Party Transaction [Line Items]
Investment in related party	$ 5,000,000.0							$ 5,000,000.0		$ 5,000,000.0	$ 5,000,000.0		$ 5,000,000
Director | Hedge fund Managed by Leucadia | Affiliated Entity
Related Party Transaction [Line Items]
Capital contribution		$ 3,600,000