Fair Value Disclosures (Fair Value Option Election Narrative) (Details) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) director shares	Jun. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Apr. 30, 2017 $ / shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
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	$ 62,600		$ 62,600					$ 29,800
90 days or more past due	41,900		41,900					18,900
Securities borrowed	7,758,532		7,758,532					7,743,562
Securities loaned	2,763,253		2,763,253					2,819,132
Investment in associated company	2,350,980	$ 2,105,088	2,350,980		$ 2,105,088			2,125,098	$ 1,757,369
Financial instruments owned trading assets, at fair value	15,505,065		15,505,065					14,985,237
KCG Holdings [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Changes in fair value of investments reflected as principal transactions	2,200	6,100	93,400		24,600
Securities borrowed								9,200
Securities loaned								$ 9,200
Business acquisition, share price (in USD per share) | $ / shares							$ 20.00
HRG [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Changes in fair value of investments reflected as principal transactions	$ (97,900)	$ 91,800	$ 2,300		$ 99,700
Percentage of outstanding common stock owned	23.00%		23.00%					23.00%
Shares owned, number | shares	46.6		46.6					46.6
Financial instruments owned trading assets, at fair value	$ 727,400		$ 727,400					$ 725,100
Cash consideration paid for shares	$ 475,600		$ 475,600
Revenue of investee				$ 3,686,700		$ 3,798,800
Net income from continuing operations of investee				53,800		152,500
Net income (loss) of investee				249,200		(70,100)
Net income (loss) attributable to HRG				$ 132,200		$ (191,500)
Number of directors appointed | director			2