Investments - Jefferies Finance - Narrative (Detail) - Jefferies Finance, LLC - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Jul. 31, 2017	Aug. 31, 2017	Nov. 30, 2016
Guarantee Obligations [Line Items]
Increase of equity commitment	$ 150.0
Equity commitment	750.0	$ 750.0
Equity commitment, contribution	$ 74.8
Total committed equity capitalization of JIFN		1,500.0
Funded portion of equity commitment to subsidiary		612.1
Unfunded portion of equity commitment to subsidiary		$ 137.9
Extension period		1 year
Termination notice period		60 days
Funded portion of loan commitment		$ 35.1
Loan commitment		250.0
Corporate debt securities
Guarantee Obligations [Line Items]
Committed line of credit facility amount		500.0
Other Assets
Guarantee Obligations [Line Items]
Receivables under service agreement		$ 22.5
Accrued expenses and other liabilities
Guarantee Obligations [Line Items]
Payables under service agreement			$ 5.8