Document and Entity Information - shares	6 Months Ended
	Dec. 31, 2020	Jan. 31, 2021
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	001-31298
Entity Registrant Name	LANNETT CO INC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	23-0787699
Entity Address, Address Line One	9000 State Road
Entity Address, City or Town	Philadelphia
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19136
City Area Code	215
Local Phone Number	333-9000
Title of 12(b) Security	Common Stock
Trading Symbol	LCI
Security Exchange Name	NYSE
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		41,401,730
Entity Central Index Key	0000057725
Current Fiscal Year End Date	--06-30
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false