Document and Entity Information - shares	9 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Document and Entity Information
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Entity Registrant Name	LANNETT CO INC
Amendment Flag	false
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 Common Stock, Shares Outstanding		40,350,852
Entity Central Index Key	0000057725
Current Fiscal Year End Date	--06-30
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3