| Cover | Dec. 13, 2019 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 13, 2019 |
| Entity File Number | 001-31573 |
| Entity Registrant Name | MEDIFAST, INC. |
| Entity Central Index Key | 0000910329 |
| Entity Tax Identification Number | 13-3714405 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 100 International Drive |
| Entity Address, City or Town | Baltimore |
| Entity Address, State or Province | MD |
| Entity Address, Postal Zip Code | 21202 |
| City Area Code | 410 |
| Local Phone Number | 581-8042 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.001 per share |
| Trading Symbol | MED |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
