Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Earnings (Loss) Per Common Share
Net income (loss) attributable to Lannett Company, Inc	$ (11,359)	$ 12,770	$ 14,022	$ 13,257	$ 5,726	$ 14,929	$ 8,172	$ (29,408)	$ 3,571	$ (5,490)	$ 13,520	$ 33,181	$ 28,690	$ (581)	$ 44,782
Basic weighted average common shares outstanding													37,127,306	36,812,524	36,442,782
Effect of potentially dilutive stock options, warrants and restricted stock awards													1,035,208		946,663
Diluted weighted average common shares outstanding													38,162,514	36,812,524	37,389,445
Earnings (loss) per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)	$ (0.30)	$ 0.34	$ 0.38	$ 0.36	$ 0.16	$ 0.41	$ 0.22	$ (0.80)	$ 0.10	$ (0.15)	$ 0.37	$ 0.91	$ 0.77	$ (0.02)	$ 1.23
Diluted (in dollars per share)	$ (0.30)	$ 0.33	$ 0.37	$ 0.35	$ 0.15	$ 0.40	$ 0.22	$ (0.80)	$ 0.10	$ (0.15)	$ 0.36	$ 0.89	$ 0.75	$ (0.02)	$ 1.20
Anti-dilutive shares excluded in the computation of diluted earnings per share													3,000,000	4,300,000	3,000,000