Document and Entity Information - USD ($)	12 Months Ended
	Jun. 30, 2020	Jul. 31, 2020	Dec. 31, 2019
Document and Entity Information
Document Type	10-K
Document Period End Date	Jun. 30, 2020
Entity Registrant Name	LANNETT CO INC
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 277,527,086
Entity Common Stock, Shares Outstanding		40,220,659
Entity Central Index Key	0000057725
Current Fiscal Year End Date	--06-30
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY