REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 472,581	$ 564,764
United States
Disaggregation of Revenue [Line Items]
Revenue	452,873	535,943
Foreign
Disaggregation of Revenue [Line Items]
Revenue	19,708	28,821
Manufacturing / Wholesale | Third-party contract manufacturing
Disaggregation of Revenue [Line Items]
Revenue	0	15,783
Manufacturing / Wholesale | Wholesale partner sales
Disaggregation of Revenue [Line Items]
Revenue	14,855	18,901
Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	472,581	600,269
Operating Segment | U.S. and Canada
Disaggregation of Revenue [Line Items]
Revenue	424,181	489,157
Operating Segment | U.S. and Canada | Product Sales
Disaggregation of Revenue [Line Items]
Revenue	327,720	377,374
Operating Segment | U.S. and Canada | Protein
Disaggregation of Revenue [Line Items]
Revenue	73,808	80,257
Operating Segment | U.S. and Canada | Performance supplements
Disaggregation of Revenue [Line Items]
Revenue	67,992	74,778
Operating Segment | U.S. and Canada | Weight management
Disaggregation of Revenue [Line Items]
Revenue	20,516	30,779
Operating Segment | U.S. and Canada | Vitamins
Disaggregation of Revenue [Line Items]
Revenue	48,962	47,056
Operating Segment | U.S. and Canada | Herbs / Greens
Disaggregation of Revenue [Line Items]
Revenue	13,805	15,873
Operating Segment | U.S. and Canada | Wellness
Disaggregation of Revenue [Line Items]
Revenue	39,082	47,200
Operating Segment | U.S. and Canada | Health / Beauty
Disaggregation of Revenue [Line Items]
Revenue	39,485	46,388
Operating Segment | U.S. and Canada | Food / Drink
Disaggregation of Revenue [Line Items]
Revenue	19,199	28,243
Operating Segment | U.S. and Canada | General merchandise
Disaggregation of Revenue [Line Items]
Revenue	4,871	6,800
Operating Segment | U.S. and Canada | Wholesale sales to franchisees
Disaggregation of Revenue [Line Items]
Revenue	51,056	58,257
Operating Segment | U.S. and Canada | Royalties and franchise fees
Disaggregation of Revenue [Line Items]
Revenue	7,327	8,472
Operating Segment | U.S. and Canada | Sublease income
Disaggregation of Revenue [Line Items]
Revenue	10,242	10,976
Operating Segment | U.S. and Canada | Cooperative advertising and other franchise support fees
Disaggregation of Revenue [Line Items]
Revenue	4,408	5,067
Operating Segment | U.S. and Canada | Other
Disaggregation of Revenue [Line Items]
Revenue	23,428	29,011
Operating Segment | International
Disaggregation of Revenue [Line Items]
Revenue	33,545	40,923
Operating Segment | International | Wholesale sales to franchisees
Disaggregation of Revenue [Line Items]
Revenue	20,183	25,437
Operating Segment | International | Royalties and franchise fees
Disaggregation of Revenue [Line Items]
Revenue	6,508	6,202
Operating Segment | International | Other
Disaggregation of Revenue [Line Items]
Revenue	6,854	9,284
Operating Segment | Manufacturing / Wholesale
Disaggregation of Revenue [Line Items]
Revenue	14,855	70,189
Operating Segment | Manufacturing / Wholesale | Third-party contract manufacturing
Disaggregation of Revenue [Line Items]
Revenue	0	15,783
Operating Segment | Manufacturing / Wholesale | Wholesale partner sales
Disaggregation of Revenue [Line Items]
Revenue	14,855	18,901
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	0	(35,505)
Intersegment Eliminations | Manufacturing / Wholesale
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ (35,505)