Earnings (Loss) Per Common Share (Earnings Per Share Computation) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator for earnings (loss) per share:
Net income (loss) attributable to Leucadia National Corporation common shareholders	$ 99,351	$ 154,358	$ 438,952	$ (11,233)
Allocation of earnings to participating securities	(368)	(2,060)	(1,692)	0
Net income (loss) attributable to Leucadia National Corporation common shareholders for basic earnings (loss) per share	98,983	152,298	437,260	(11,233)
Adjustment to allocation of earnings to participating securities related to diluted shares	(2)	6	3	0
Mandatorily redeemable convertible preferred share dividends	0	1,016	3,203	0
Net income (loss) attributable to Leucadia National Corporation common shareholders for diluted earnings (loss) per share	$ 98,981	$ 153,320	$ 440,466	$ (11,233)
Denominator for earnings (loss) per share:
Denominator for basic earnings (loss) per share – weighted average shares (in shares)	367,828,000	370,404,000	368,736,000	371,814,000
Dilutive effect of share-based payment awards (in shares)	23,000	1,000	22,000	0
Warrants (in shares)	0	0	0	0
Mandatorily redeemable convertible preferred shares (in shares)	0	4,162,000	4,162,000	0
Denominator for diluted earnings (loss) per share (in shares)	370,198,000	374,567,000	375,233,000	371,814,000
Weighted average shares of participating securities (in shares)	1,366,700	5,009,500	1,433,500	4,859,900
3.875% Convertible Senior Debentures, due November 1, 2029 [Member]
Denominator for earnings (loss) per share:
Convertible Senior Debenture (in shares)	0	0	0	0
Senior Executive Compensation Plan [Member]
Denominator for earnings (loss) per share:
Dilutive effect of share-based payment awards (in shares)	2,347,000	0	2,313,000	0