Loans to and Investments in Associated Companies (Schedule of Loans to and Investments In Associated Companies) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
May 31, 2020	May 31, 2019	May 31, 2020	May 31, 2019
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			$ 1,652,957	$ 2,417,332
Income (losses) related to associated companies	$ (6,721)	$ 22,170	(74,576)	49,483
Income (losses) related to Jefferies associated companies	(54,895)	42,984	(26,136)	54,321
Contributions to (distributions from) associated companies, net			(5,743)	(102,666)
Other			13,291	(2,576)
Loans to and investments in associated companies as of end of period	1,559,793	2,415,894	1,559,793	2,415,894
Jefferies Finance
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			673,867	728,560
Income (losses) related to associated companies			0	0
Income (losses) related to Jefferies associated companies	(53,069)	14,935	(47,950)	7,936
Contributions to (distributions from) associated companies, net			27,547	(63,070)
Other			0	0
Loans to and investments in associated companies as of end of period	653,464	673,426	653,464	673,426
Berkadia
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			268,949	245,228
Income (losses) related to associated companies			0	0
Income (losses) related to Jefferies associated companies	31	25,296	21,925	47,945
Contributions to (distributions from) associated companies, net			(36,562)	(18,124)
Other			472	515
Loans to and investments in associated companies as of end of period	254,784	275,564	254,784	275,564
National Beef
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period				653,630
Income (losses) related to associated companies	0	34,946	0	62,051
Income (losses) related to Jefferies associated companies				0
Contributions to (distributions from) associated companies, net				(54,940)
Other				(9)
Loans to and investments in associated companies as of end of period		660,732		660,732
FXCM
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			70,223	75,031
Income (losses) related to associated companies	7,890	(2,300)	6,252	(5,016)
Income (losses) related to Jefferies associated companies			0	0
Contributions to (distributions from) associated companies, net			0	0
Other			(243)	10
Loans to and investments in associated companies as of end of period	76,232	70,025	76,232	70,025
Linkem
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			194,847	165,157
Income (losses) related to associated companies	(6,624)	(6,960)	(19,809)	(8,581)
Income (losses) related to Jefferies associated companies			0	0
Contributions to (distributions from) associated companies, net			35,242	49,590
Other			3,825	(3,973)
Loans to and investments in associated companies as of end of period	214,105	202,193	214,105	202,193
HomeFed
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period				337,542
Income (losses) related to associated companies	0	(2,500)	0	(517)
Income (losses) related to Jefferies associated companies				0
Contributions to (distributions from) associated companies, net				0
Other				0
Loans to and investments in associated companies as of end of period		337,025		337,025
Real estate associated companies
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			255,309	87,074
Income (losses) related to associated companies	(428)	(1,524)	(53,442)	1,072
Income (losses) related to Jefferies associated companies			0	0
Contributions to (distributions from) associated companies, net			(31,784)	0
Other			0	0
Loans to and investments in associated companies as of end of period	170,083	88,146	170,083	88,146
Other
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			189,762	125,110
Income (losses) related to associated companies	(7,559)	508	(7,577)	474
Income (losses) related to Jefferies associated companies	(1,857)	2,753	(111)	(1,560)
Contributions to (distributions from) associated companies, net			(186)	(16,122)
Other			9,237	881
Loans to and investments in associated companies as of end of period	191,125	$ 108,783	191,125	$ 108,783
Linkem and Other \| Loans and debt securities
Equity Method Investment [Roll Forward]
Loans to and investments in associated companies as of beginning of period			70,200
Loans to and investments in associated companies as of end of period	92,300		92,300
Brooklyn Renaissance Plaza and Hotel \| HomeFed
Equity Method Investment [Roll Forward]
Equity method investment, other than temporary impairment	$ 6,900		6,900
RedSky JZ Fulton Mall \| HomeFed
Equity Method Investment [Roll Forward]
Equity method investment, other than temporary impairment			$ 55,600

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