Fair Value Disclosures - Additional Information (Details) $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) director shares	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Securities borrowed	$ 7,721,803		$ 7,743,562
Securities loaned	2,843,911		2,819,132
Trading assets, at fair value	15,512,730		14,985,237
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	578,014		857,337
Jefferies Plan
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Aggregate fair value of loans and other receivables on nonaccrual status and/or greater than 90 days past due	55,100		29,800
Aggregate fair value of loans and other receivables greater than 90 days past due	37,400		18,900
KCG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Changes in fair value of investments reflected as principal transactions	93,400		19,600		$ 49,100
Advisory fees			2,900
Securities borrowed			9,200
Securities loaned			9,200
HRG
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Changes in fair value of investments reflected as principal transactions	$ 64,800		$ 93,200		$ (28,000)
Shares owned, number | shares	46.6		46.6
Percentage of outstanding common stock owned	23.00%		23.00%
Trading assets, at fair value	$ 789,900		$ 725,100
Cash consideration paid for shares	$ 475,600
Number of directors appointed | director	2
Revenue of investee		$ 5,008,500		$ 5,048,600		$ 4,753,800
Net income (loss) from continuing operations of investee		102,900		144,200		(219,700)
Net income (loss) of investee		273,200		(33,900)		(512,400)
Net income (loss) attributable to HRG		$ 106,000		$ (198,800)		$ (556,800)
Level 1 | US Treasury securities
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	$ 99,700		$ 99,900