Segment Information (Schedule Of Segment Reporting Information, By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	May 31, 2019	Jun. 30, 2018	May 31, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net Revenues	$ 1,101,657	$ 911,159	$ 1,930,100	$ 1,806,594
Consolidated income before income taxes	183,479	37,515	232,796	75,278
Depreciation and amortization	36,786	31,905	70,720	60,065
Parent Company interest
Segment Reporting Information [Line Items]
Consolidated income before income taxes	(14,766)	(14,750)	(29,528)	(29,496)
LAM and Berkadia Transferred
Segment Reporting Information [Line Items]
Net Revenues		15,800		(20,800)
Consolidated income before income taxes		29,800		9,100
Reportable Segments
Segment Reporting Information [Line Items]
Net Revenues	1,098,149	911,968	1,924,398	1,810,182
Consolidated income before income taxes	192,477	50,592	253,824	102,548
Reportable Segments | Jefferies Group
Segment Reporting Information [Line Items]
Net Revenues	901,851	822,557	1,587,569	1,643,803
Consolidated income before income taxes	155,138	121,865	217,723	244,603
Depreciation and amortization	18,968	17,288	36,630	33,654
Reportable Segments | Merchant Banking
Segment Reporting Information [Line Items]
Net Revenues	187,324	86,417	323,662	160,318
Consolidated income before income taxes	51,224	(50,058)	71,329	(99,315)
Depreciation and amortization	16,951	13,740	32,368	24,664
Reportable Segments | Corporate
Segment Reporting Information [Line Items]
Net Revenues	8,974	2,994	13,167	6,061
Consolidated income before income taxes	(13,885)	(21,215)	(35,228)	(42,740)
Depreciation and amortization	867	877	1,722	1,747
Consolidation adjustments
Segment Reporting Information [Line Items]
Net Revenues	3,508	(809)	5,702	(3,588)
Consolidated income before income taxes	$ 5,768	$ 1,673	$ 8,500	$ 2,226