Business Segments (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 356,706,000	$ 298,189,000	$ 257,552,000
Cost of Sales	88,671,000	73,693,000	65,083,000
Selling, General and Administrative Expense	233,568,000	188,770,000	154,971,000
Depreciation and Amortization	11,205,000	8,344,000	5,859,000
Interest(net) and other	(1,196,000)	(298,000)	(52,000)
Income before income taxes	24,458,000	27,680,000	31,692,000
Segment Assets	130,251,000	105,665,000	94,059,000
Medifast Inc
Segment Reporting Information [Line Items]
Revenues	300,511,000	259,191,000	229,879,000
Cost of Sales	74,984,000	63,888,000	58,795,000
Selling, General and Administrative Expense	184,615,000	152,647,000	135,441,000
Depreciation and Amortization	8,081,000	6,416,000	4,765,000
Interest(net) and other	141,000	30,000	105,000
Income before income taxes	32,690,000	36,210,000	30,773,000
Segment Assets	86,944,000	64,388,000	55,858,000
Mwcc And Wholesale
Segment Reporting Information [Line Items]
Revenues	56,195,000	38,998,000	27,673,000
Cost of Sales	13,687,000	9,805,000	6,288,000
Selling, General and Administrative Expense	40,194,000	30,335,000	13,837,000
Depreciation and Amortization	2,864,000	1,596,000	786,000
Interest(net) and other	26,000	0	0
Income before income taxes	(576,000)	(2,738,000)	6,762,000
Segment Assets	14,610,000	12,658,000	9,301,000
Other Entity
Segment Reporting Information [Line Items]
Revenues	0	0	0
Cost of Sales	0	0	0
Selling, General and Administrative Expense	8,759,000	5,788,000	5,693,000
Depreciation and Amortization	260,000	332,000	307,000
Interest(net) and other	(1,363,000)	(328,000)	(157,000)
Income before income taxes	(7,656,000)	(5,792,000)	(5,843,000)
Segment Assets	$ 28,697,000	$ 28,619,000	$ 28,900,000