Segment Information (Schedule Of Segment Reporting Information, By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net Revenues	$ 2,496,216	$ 2,366,096	$ 2,839,463	$ 3,184,683	$ 2,688,355	$ 3,003,643	$ 2,851,963	$ 2,942,524	$ 10,886,458	$ 11,486,485	$ 10,425,746
Total consolidated pre-tax income from continuing operations									356,536	381,222	545,585
Depreciation and amortization									224,133	185,993	167,425
Assets	46,339,812				52,623,908				46,339,812	52,623,908	47,866,781
Unrealized and realized gains and interest income									642,824	662,213	574,895
Deferred tax asset, net	1,575,368				1,712,535				1,575,368	1,712,535
FXCM [Member]
Segment Reporting Information [Line Items]
Unrealized and realized gains and interest income									491,300
Jefferies [Member]
Segment Reporting Information [Line Items]
Deferred tax asset, net	320,200				399,600				320,200	399,600	524,800
Parent Company Interest [Member]
Segment Reporting Information [Line Items]
Net Revenues									(21,000)	0	0
Assets	(149,723)				(53,405)				(149,723)	(53,405)	(83,218)
Parent Company Interest [Member]
Segment Reporting Information [Line Items]
Total consolidated pre-tax income from continuing operations									(85,884)	(98,115)	(72,217)
Jefferies [Member]
Segment Reporting Information [Line Items]
Net Revenues									2,476,133	2,986,325	2,134,002
Total consolidated pre-tax income from continuing operations									119,165	358,396	260,984
Depreciation and amortization									92,165	78,566	59,631
Assets	38,608,956				44,563,808				38,608,956	44,563,808	40,168,572
National Beef [Member]
Segment Reporting Information [Line Items]
Net Revenues									7,402,419	7,832,424	7,487,724
Total consolidated pre-tax income from continuing operations									(123,915)	(40,303)	(42,358)
Depreciation and amortization									89,317	85,305	88,484
Assets	1,516,130				1,718,521				1,516,130	1,718,521	1,703,662
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net Revenues									78,122	60,720	50,190
Total consolidated pre-tax income from continuing operations									(45,592)	(144,508)	(91,917)
Depreciation and amortization									3,744	5,627	9,924
Assets	1,778,987				3,240,561				1,778,987	3,240,561	4,515,768
Total Reportable Segment [Member]
Segment Reporting Information [Line Items]
Net Revenues									9,956,674	10,879,469	9,671,916
Total consolidated pre-tax income from continuing operations									(50,342)	173,585	126,709
Depreciation and amortization									185,226	169,498	158,039
Assets	41,904,073				49,522,890				41,904,073	49,522,890	46,388,002
All other [Member]
Segment Reporting Information [Line Items]
Net Revenues									950,784	607,016	753,830
Total consolidated pre-tax income from continuing operations									492,762	305,752	491,093
Depreciation and amortization									38,907	16,495	9,386
Assets	$ 4,585,462				$ 3,154,423				$ 4,585,462	$ 3,154,423	$ 1,561,997