Fair Value Disclosures (Fair Value Option Election Narrative) (Details) $ in Thousands, shares in Millions	3 Months Ended
	Feb. 28, 2019 USD ($) director shares	Dec. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2017 USD ($) shares	Nov. 30, 2018 USD ($)	Jul. 13, 2018
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Financial instruments owned trading assets, at fair value	$ 17,925,044					$ 17,463,256
Jefferies Group
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Loans and other receivables on nonaccrual status and/or 90 days or greater past due	165,700					105,300
Loans and other receivables 90 days or greater past due	43,700					19,400
HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Cash consideration paid for shares	$ 475,600
Revenue of investee					$ 646,500
Net income (loss) from continuing operations of investee					78,100
Net income (loss) of investee					578,900
Net income attributable to HRG controlling interest					$ 507,400
Number of directors appointed by Company | director	1
Spectrum Brands
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Financial instruments owned trading assets, at fair value	$ 407,100					371,100
HRG Group/Spectrum Brands Holdings, Inc.
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Changes in fair value of investments reflected as principal transactions	$ 36,000		$ (21,400)
Fiesta Restaurant Group, Inc.
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Revenue of investee		$ 167,600		$ 162,200
Net income (loss) from continuing operations of investee		7,900		10,800
Net income (loss) of investee		$ 7,900		$ 10,800
Number of directors appointed by Company | director	1
HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Shares owned, number | shares				46.6	46.6
Percentage of outstanding common stock owned				23.00%	23.00%
Ownership percentage				23.00%	23.00%
Spectrum Brands
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Shares owned, number | shares	7.5
Ownership percentage	15.00%						14.00%
Spectrum Brands | HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Ownership percentage							62.00%
Fiesta Restaurant Group, Inc.
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Shares owned, number | shares	3.8
Percentage of outstanding common stock owned	14.00%
Financial instruments owned trading assets, at fair value	$ 57,100					$ 71,400
Changes in fair value of investments reflected as principal transactions	$ (14,300)		$ (200)