Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2020	Apr. 29, 2020
Document Type	10-Q
Document Quarterly Report 1	true
Document Period End Date	Mar. 31, 2020
Document Transition Report 1	false
Entity File Number	001-31573
Entity Registrant Name	Medifast, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3714405
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
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		11,780,970
Entity Central Index Key	0000910329
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock [Member]
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	MED
Security Exchange Name	NYSE
Preferred Stock [Member]
Title of 12(b) Security	Preferred Stock Purchase Rights
No Trading Symbol Flag	true
Security Exchange Name	NYSE