Loans To And Investments In Associated Companies (Schedule Of Loans to and Investments In Associated Companies) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 01, 2016	Dec. 31, 2015
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			$ 1,757,369	$ 1,712,568
Income (losses) related to associated companies	$ 36,503	$ 24,243	108,445	94,501
Income (losses) related to associated companies classified as other revenues	15,390	38,545	(15,862)	87,691
Contributions to (distributions from) associated companies, net			(84,051)	(175,303)
Other, including foreign exchange and unrealized gains (losses)			339,187	(15,711)
Loans to and investments in associated companies, ending balance	2,105,088	1,703,746	2,105,088	1,703,746
Noncontrolling interests	177,807		177,807			$ 64,679
Jefferies Finance [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			528,575	508,891
Income (losses) related to associated companies			0	0
Income (losses) related to associated companies classified as other revenues	12,481	26,714	(26,000)	58,245
Contributions to (distributions from) associated companies, net			(19,300)	(40,500)
Other, including foreign exchange and unrealized gains (losses)			0	2
Loans to and investments in associated companies, ending balance	$ 483,275	526,638	$ 483,275	526,638
Percentage of ownership owned	50.00%		50.00%
Jefferies LoanCore [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			$ 288,741	258,947
Income (losses) related to associated companies			0	0
Income (losses) related to associated companies classified as other revenues	$ 3,172	12,510	11,186	30,604
Contributions to (distributions from) associated companies, net			(133,635)	(43,280)
Other, including foreign exchange and unrealized gains (losses)			0	1
Loans to and investments in associated companies, ending balance	$ 166,292	246,272	$ 166,292	246,272
Percentage of ownership owned	48.50%		48.50%
Berkadia [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			$ 190,986	208,511
Income (losses) related to associated companies	$ 26,004	15,730	59,456	67,806
Income (losses) related to associated companies classified as other revenues			0	0
Contributions to (distributions from) associated companies, net			(70,847)	(72,143)
Other, including foreign exchange and unrealized gains (losses)			291	(5,464)
Loans to and investments in associated companies, ending balance	$ 179,886	198,710	$ 179,886	198,710
Percentage of ownership owned	50.00%		50.00%
FXCM [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			$ 0
Income (losses) related to associated companies			0
Income (losses) related to associated companies classified as other revenues			0
Contributions to (distributions from) associated companies, net			0
Other, including foreign exchange and unrealized gains (losses)			334,500
Loans to and investments in associated companies, ending balance	$ 334,500		334,500
Garcadia [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			172,660	167,939
Income (losses) related to associated companies	14,233	16,342	43,501	47,476
Income (losses) related to associated companies classified as other revenues			0	0
Contributions to (distributions from) associated companies, net			(22,562)	(45,813)
Other, including foreign exchange and unrealized gains (losses)			0	0
Loans to and investments in associated companies, ending balance	$ 193,599	169,602	$ 193,599	169,602
Percentage of ownership owned	75.00%		75.00%
Linkem [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			$ 150,149	159,054
Income (losses) related to associated companies	$ (5,836)	(4,750)	(20,709)	(13,892)
Income (losses) related to associated companies classified as other revenues			0	0
Contributions to (distributions from) associated companies, net			33,297	6,931
Other, including foreign exchange and unrealized gains (losses)			4,155	(10,403)
Loans to and investments in associated companies, ending balance	$ 166,892	141,690	$ 166,892	141,690
Percentage of ownership owned	42.00%		42.00%
HomeFed Corporation [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			$ 275,378	271,782
Income (losses) related to associated companies	$ 800	1,338	23,146	(1,714)
Income (losses) related to associated companies classified as other revenues			0	0
Contributions to (distributions from) associated companies, net			0	0
Other, including foreign exchange and unrealized gains (losses)			0	0
Loans to and investments in associated companies, ending balance	$ 298,524	270,068	$ 298,524	270,068
Percentage of ownership owned	65.00%		65.00%
Golden Queen Mining Company, LLC [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			$ 114,323	103,598
Income (losses) related to associated companies	$ 56	(279)	(1,608)	(1,278)
Income (losses) related to associated companies classified as other revenues			0	0
Contributions to (distributions from) associated companies, net			0	12,500
Other, including foreign exchange and unrealized gains (losses)			0	0
Loans to and investments in associated companies, ending balance	$ 112,715	114,820	$ 112,715	114,820
Percentage of ownership owned	35.00%		35.00%
Noncontrolling interests	$ 33,200		$ 33,200			$ 33,700
54 Madison [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			0
Income (losses) related to associated companies	906	0	3,389	0
Income (losses) related to associated companies classified as other revenues			0
Contributions to (distributions from) associated companies, net			123,731
Other, including foreign exchange and unrealized gains (losses)			3,642
Loans to and investments in associated companies, ending balance	$ 130,762		$ 130,762
Percentage of ownership owned	48.10%		48.10%
Noncontrolling interests	$ 78,000		$ 78,000
Other [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Loans to and investments in associated companies, beginning balance			36,557	33,846
Income (losses) related to associated companies	340	(4,138)	1,270	(3,897)
Income (losses) related to associated companies classified as other revenues	(263)	(679)	(1,048)	(1,158)
Contributions to (distributions from) associated companies, net			5,265	7,002
Other, including foreign exchange and unrealized gains (losses)			(3,401)	153
Loans to and investments in associated companies, ending balance	$ 38,643	$ 35,946	$ 38,643	$ 35,946
Investment in FXCM [Member]
Loans to and Investments in Associated Companies Rollforward [Roll Forward]
Percentage of ownership owned	49.90%		49.90%		49.90%