Related Party Transactions - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 24, 2017	Dec. 31, 2016	Feb. 28, 2017	Feb. 29, 2016	Nov. 30, 2016
Related Party Transaction [Line Items]
Purchase commitments from Berkadia Commercial Mortgage, LLC			$ 654,200,000		$ 817,000,000
Loans outstanding to certain employees			37,500,000		38,400,000
Financial instruments, owned, at fair value			13,252,736,000		13,809,512,000
Equity Method Investee [Member] | Equity Investments in Jefferies Capital Partners Related Funds [Member]
Related Party Transaction [Line Items]
Equity investments loans in related funds			36,700,000		37,700,000
Leucadia [Member] | Other Assets [Member]
Related Party Transaction [Line Items]
Tax receivable			155,400,000		80,100,000
Leucadia [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Revenue from related parties			6,100,000	$ 7,600,000
Due from related party			1,600,000		2,800,000
Due to related party			2,600,000		1,900,000
Proceeds from sale of securities	$ 25,600,000
Gain (loss) on sale of securities	$ 0
Leucadia [Member] | Affiliated Entity [Member] | Asset Management Income [Member]
Related Party Transaction [Line Items]
Revenue from related parties				$ 100,000
Hedge Fund Managed by Subsidiary of Leucadia [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Capital redemption		$ 17,000,000
Corporate debt securities [Member] | Leucadia [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Financial instruments, owned, at fair value			$ 1,800,000		$ 1,000,000