Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 14, 2020	Jun. 28, 2019
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Title of 12(b) Security	Common Stock, $0.001 par value per share
Document Period End Date	Dec. 31, 2019
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
Trading Symbol	MED
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		11,765,154
Entity Central Index Key	0000910329
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 1.5