Common Share and Earnings Per Common Share (Earnings Per Share Computation) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
May 31, 2019	Jun. 30, 2018	May 31, 2019	Jun. 30, 2018
Numerator for earnings per share:
Net income attributable to Jefferies Financial Group Inc. common shareholders	$ 670,764	$ 725,529	$ 715,575	$ 850,054
Allocation of earnings to participating securities	(4,086)	(3,870)	(4,241)	(3,831)
Net income attributable to Jefferies Financial Group Inc. common shareholders for basic earnings per share	666,678	721,659	711,334	846,223
Adjustment to allocation of earnings to participating securities related to diluted shares	43	37	34	29
Mandatorily redeemable convertible preferred share dividends	1,276	0	2,552	0
Net income attributable to Jefferies Financial Group Inc. common shareholders for diluted earnings per share	$ 667,997	$ 721,696	$ 713,920	$ 846,252
Denominator for earnings per share:
Weighted average common shares outstanding	293,600,000	342,719,000	299,067,000	349,647,000
Denominator for basic earnings per share – weighted average shares	307,010,000	352,049,000	311,108,000	359,237,000
Mandatorily redeemable convertible preferred shares (in shares)	4,162,000	0	4,162,000	0
Denominator for diluted earnings (loss) per share (in shares)	312,527,000	356,075,000	317,736,000	362,685,000
Weighted average shares of participating securities (in shares)	1,881,600	1,887,100	1,856,400	1,603,500
Restricted Stock with Future Service Required
Denominator for earnings per share:
Weighted average shares of restricted stock outstanding with future service required	(1,873,000)	(1,868,000)	(1,851,000)	(1,578,000)
Restricted Stock Units with No Future Service Required
Denominator for earnings per share:
Weighted average RSUs outstanding with no future service required (in shares)	15,283,000	11,198,000	13,892,000	11,168,000
Stock options
Denominator for earnings per share:
Dilutive effect of share-based payment awards (in shares)	0	7,000	0	18,000
Restricted Stock Units \| Senior Executive Compensation Plan
Denominator for earnings per share:
Dilutive effect of share-based payment awards (in shares)	1,355,000	4,019,000	2,466,000	3,430,000

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