Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	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, 2019	Jun. 30, 2018	Jun. 30, 2017
Earnings (Loss) Per Common Share
Net income (loss) attributable to Lannett Company, Inc.	$ (7,586)	$ 10,645	$ 12,362	$ (287,528)	$ (11,359)	$ 12,770	$ 14,022	$ 13,257	$ 5,726	$ 14,929	$ 8,172	$ (29,408)	$ (272,107)	$ 28,690	$ (581)
Basic weighted average common shares outstanding													37,779,812	37,127,306	36,812,524
Effect of potentially dilutive options and restricted stock awards														1,035,208
Diluted weighted average common shares outstanding													37,779,812	38,162,514	36,812,524
Earnings (loss) per common share attributable to Lannett Company, Inc.:
Basic (in dollars per share)	$ (0.20)	$ 0.28	$ 0.33	$ (7.65)	$ (0.30)	$ 0.34	$ 0.38	$ 0.36	$ 0.16	$ 0.41	$ 0.22	$ (0.80)	$ (7.20)	$ 0.77	$ (0.02)
Diluted (in dollars per share)	$ (0.20)	$ 0.27	$ 0.32	$ (7.65)	$ (0.30)	$ 0.33	$ 0.37	$ 0.35	$ 0.15	$ 0.40	$ 0.22	$ (0.80)	$ (7.20)	$ 0.75	$ (0.02)
Anti-dilutive shares excluded in the computation of diluted earnings per share													1,900,000	3,000,000	4,300,000