Fair Value Disclosures (Fair Value Option Election Narrative) (Details) $ in Thousands, shares in Millions	2 Months Ended	12 Months Ended
	Feb. 28, 2013 USD ($)	Dec. 31, 2015 USD ($) director shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
90 days or more past due		$ 11,300	$ 0
Aggregate fair value of loans and other receivables on nonaccrual status		307,500	274,600
Trading assets, at fair value		18,293,090	19,612,490
Jefferies [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	$ 182,700
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		49,100	(14,700)	$ 19,500
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		$ (28,000)	119,200
Shares owned, number | shares		46.6
Percentage of outstanding common stock owned		23.00%
Trading assets, at fair value		$ 631,900	$ 659,900
Cash consideration paid for shares		$ 475,600
Number of directors appointed | director		2
Maximum ownership percentage		27.50%
Restriction on sale, maximum percentage		4.90%