REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 564,764	$ 607,533
Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	600,269	672,196
Operating Segment | U.S. and Canada
Disaggregation of Revenue [Line Items]
Revenue	489,157	512,414
Operating Segment | U.S. and Canada | Product Sales
Disaggregation of Revenue [Line Items]
Revenue	377,374	397,779
Operating Segment | U.S. and Canada | Protein
Disaggregation of Revenue [Line Items]
Revenue	80,257	87,670
Operating Segment | U.S. and Canada | Performance supplements
Disaggregation of Revenue [Line Items]
Revenue	74,778	75,616
Operating Segment | U.S. and Canada | Weight management
Disaggregation of Revenue [Line Items]
Revenue	30,779	39,787
Operating Segment | U.S. and Canada | Weight management
Disaggregation of Revenue [Line Items]
Revenue	47,056	50,371
Operating Segment | U.S. and Canada | Herbs / Greens
Disaggregation of Revenue [Line Items]
Revenue	15,873	16,158
Operating Segment | U.S. and Canada | Wellness
Disaggregation of Revenue [Line Items]
Revenue	47,200	47,701
Operating Segment | U.S. and Canada | Health / Beauty
Disaggregation of Revenue [Line Items]
Revenue	46,388	48,054
Operating Segment | U.S. and Canada | Food / Drink
Disaggregation of Revenue [Line Items]
Revenue	28,243	25,360
Operating Segment | U.S. and Canada | General merchandise
Disaggregation of Revenue [Line Items]
Revenue	6,800	7,062
Operating Segment | U.S. and Canada | Wholesale sales to franchisees
Disaggregation of Revenue [Line Items]
Revenue	58,257	57,160
Operating Segment | U.S. and Canada | Royalties and franchise fees
Disaggregation of Revenue [Line Items]
Revenue	8,472	8,748
Operating Segment | U.S. and Canada | Sublease income
Disaggregation of Revenue [Line Items]
Revenue	10,976	11,765
Operating Segment | U.S. and Canada | Cooperative advertising and other franchise support fees
Disaggregation of Revenue [Line Items]
Revenue	5,067	5,533
Operating Segment | U.S. and Canada | Other
Disaggregation of Revenue [Line Items]
Revenue	29,011	31,429
Operating Segment | International
Disaggregation of Revenue [Line Items]
Revenue	40,923	40,065
Operating Segment | International | Wholesale sales to franchisees
Disaggregation of Revenue [Line Items]
Revenue	25,437	21,760
Operating Segment | International | Royalties and franchise fees
Disaggregation of Revenue [Line Items]
Revenue	6,202	6,621
Operating Segment | International | Other
Disaggregation of Revenue [Line Items]
Revenue	9,284	11,684
Operating Segment | Manufacturing / Wholesale
Disaggregation of Revenue [Line Items]
Revenue	70,189	119,717
Operating Segment | Manufacturing / Wholesale | Third-party contract manufacturing(1)
Disaggregation of Revenue [Line Items]
Revenue	15,783	32,722
Operating Segment | Manufacturing / Wholesale | Wholesale partner sales
Disaggregation of Revenue [Line Items]
Revenue	18,901	22,332
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(35,505)	(64,663)
Intersegment Eliminations | Manufacturing / Wholesale
Disaggregation of Revenue [Line Items]
Revenue	(35,505)	(64,663)
Intersegment Eliminations | Manufacturing / Wholesale | Intersegment sales(1)
Disaggregation of Revenue [Line Items]
Revenue	35,505	64,663
United States
Disaggregation of Revenue [Line Items]
Revenue	535,943	572,231
Foreign
Disaggregation of Revenue [Line Items]
Revenue	$ 28,821	$ 35,302