Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 182,301	$ 136,767	$ 1,070,394	$ 504,752
Other comprehensive income (loss):
Net unrealized holding gains (losses) on investments arising during the period, net of income tax provision (benefit) of $(424), $(598), $(567) and $5,106	(1,198)	(1,030)	(1,606)	8,767
Less: reclassification adjustment for net (gains) losses included in net income, net of income tax provision (benefit) of $0, $(257), $37 and $14	(2)	443	(105)	(24)
Net change in unrealized holding gains (losses) on investments, net of income tax provision (benefit) of $(424), $(341), $(604) and $5,092	(1,200)	(587)	(1,711)	8,743
Net unrealized foreign exchange gains (losses) arising during the period, net of income tax provision (benefit) of $(3,367), $4,374, $(4,160) and $12,929	(27,660)	11,250	(59,067)	49,125
Less: reclassification adjustment for foreign exchange (gains) losses included in net income, net of income tax provision (benefit) of $0, $(11), $(16) and $1,086	0	20	(20,459)	5,310
Net change in unrealized foreign exchange gains (losses), net of income tax provision (benefit) of $(3,367), $4,385, $(4,144) and $11,843	(27,660)	11,270	(79,526)	54,435
Net unrealized gains (losses) on instrument specific credit risk arising during the period, net of income tax provision (benefit) of $355, $2,149, $4,596 and $(5,270)	1,169	3,508	15,887	(8,870)
Less: reclassification adjustment for instrument specific credit risk (gains) losses included in net income, net of income tax provision (benefit) of $48, $0, $126 and $0	101	0	371	0
Net change in unrealized instrument specific credit risk gains (losses), net of income tax provision (benefit) of $307, $2,149, $4,470 and $(5,270)	1,068	3,508	15,516	(8,870)
Net change in unrealized cash flow hedges gains (losses), net of income tax provision (benefit) of $0, $0, $513 and $0	85	(1,585)	1,584	(1,585)
Reclassification adjustment for pension (gains) losses included in net income, net of income tax provision (benefit) of $(169), $(201), $(508) and $(1,835)	479	438	6,742	66
Other comprehensive income (loss), net of income taxes	(27,228)	13,044	(57,395)	52,789
Comprehensive income	155,073	149,811	1,012,999	557,541
Comprehensive (income) loss attributable to the noncontrolling interests	12,000	(28)	13,208	1,941
Comprehensive income attributable to the redeemable noncontrolling interests	(390)	(36,216)	(37,294)	(64,538)
Preferred stock dividends	(1,276)	(1,172)	(3,619)	(3,203)
Comprehensive income attributable to Jefferies Financial Group Inc. common shareholders	$ 165,407	$ 112,395	$ 985,294	$ 491,741