| Cover | Jan. 10, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 10, 2021 |
| Entity File Number | 001-31298 |
| Entity Registrant Name | LANNETT COMPANY, INC. |
| Entity Central Index Key | 0000057725 |
| Entity Tax Identification Number | 23-0787699 |
| Entity Incorporation, State or Country Code | DE |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 par value |
| Trading Symbol | LCI |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
