Fair Value Disclosures (Fair Value Option Election Narrative) (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2019 shares	Aug. 31, 2019 USD ($) director shares	Sep. 30, 2018 USD ($)	Aug. 31, 2019 USD ($) director shares	Sep. 30, 2018 USD ($)	Sep. 16, 2019 USD ($)	Nov. 30, 2018 USD ($)	Jul. 13, 2018	Dec. 31, 2017 shares
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Financial instruments owned trading assets, at fair value		$ 17,195,916		$ 17,195,916			$ 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		113,400		113,400			105,300
Loans and other receivables 90 days or greater past due		31,900		31,900			19,400
HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Cash consideration paid for shares		475,600		475,600
Spectrum Brands
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Financial instruments owned trading assets, at fair value		$ 419,800		$ 419,800			$ 371,100
Number of directors appointed by Company | director		1		1
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		$ 24,000	$ (48,500)	$ 48,800	$ (228,400)
HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Shares owned, number | shares									46,600,000
Percentage of outstanding common stock owned									23.00%
Ownership percentage									23.00%
Spectrum Brands
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Shares owned, number | shares		7,514,477		7,514,477
Ownership percentage		15.00%		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%
Subsequent event | Spectrum Brands
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Dividend distribution (in shares) | shares	7,514,477
Dividends payable						$ 451,100