Segment Information (Schedule Of Segment Reporting Information, By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net Revenues	$ 2,676,375	$ 2,366,096	$ 7,316,839	$ 8,390,242
Total consolidated pre-tax income from continuing operations	249,909	(272,185)	87,408	315,385
Depreciation and amortization	52,691	58,466	153,070	166,146
Unrealized and realized gains (losses), interest income and fees	299,066	(253,145)	458,930	548,328
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net Revenues	2,404,544	2,447,086	6,936,693	7,716,002
Total consolidated pre-tax income from continuing operations	174,840	(53,933)	161,332	2,204
Depreciation and amortization	40,075	47,617	116,596	137,964
All other [Member]
Segment Reporting Information [Line Items]
Net Revenues	271,831	(80,990)	380,146	695,240
Total consolidated pre-tax income from continuing operations	89,791	(195,271)	(29,769)	385,651
Depreciation and amortization	12,616	10,849	36,474	28,182
Parent Company interest [Member]
Segment Reporting Information [Line Items]
Total consolidated pre-tax income from continuing operations	(14,722)	(22,981)	(44,155)	(72,470)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net Revenues	0	0	0	(21,000)
Jefferies [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net Revenues	656,496	580,484	1,678,212	1,964,356
Total consolidated pre-tax income from continuing operations	83,190	3,337	(55,127)	107,606
Depreciation and amortization	16,108	24,165	45,331	68,741
National Beef [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net Revenues	1,747,042	1,864,030	5,180,127	5,714,914
Total consolidated pre-tax income from continuing operations	108,269	(31,680)	192,533	(74,665)
Depreciation and amortization	23,100	22,529	68,511	66,397
Corporate and Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net Revenues	1,006	2,572	78,354	36,732
Total consolidated pre-tax income from continuing operations	(16,619)	(25,590)	23,926	(30,737)
Depreciation and amortization	867	923	2,754	2,826
FXCM [Member]
Segment Reporting Information [Line Items]
Unrealized and realized gains (losses), interest income and fees	$ 42,800	$ (113,200)	$ (58,300)	$ 461,300

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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