REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 499,076	$ 580,185	$ 1,597,837	$ 1,805,662
United States
Disaggregation of Revenue [Line Items]
Revenue	477,306	545,332	1,526,111	1,696,887
Foreign
Disaggregation of Revenue [Line Items]
Revenue	21,770	34,853	71,726	108,775
Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	499,076	643,880	1,633,342	1,999,258
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	0	(63,695)	(35,505)	(193,596)
U.S. and Canada | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	444,734	476,519	1,409,951	1,506,250
U.S. and Canada | Product Sales | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	338,340	362,855	1,080,719	1,157,724
U.S. and Canada | Protein | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	73,103	76,738	230,520	251,480
U.S. and Canada | Performance supplements | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	70,704	68,809	218,565	217,525
U.S. and Canada | Weight management | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	22,279	29,575	82,665	108,048
U.S. and Canada | Vitamins | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	43,107	48,322	135,099	148,188
U.S. and Canada | Herbs / Greens | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	13,939	15,872	45,348	48,975
U.S. and Canada | Wellness | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	41,995	46,245	135,565	143,626
U.S. and Canada | Health / Beauty | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	44,356	43,332	137,279	138,911
U.S. and Canada | Food / Drink | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	23,806	28,325	78,308	82,394
U.S. and Canada | General merchandise | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	5,051	5,637	17,370	18,577
U.S. and Canada | Wholesale sales to franchisees | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	55,729	58,199	173,855	176,034
U.S. and Canada | Royalties and franchise fees | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	7,592	7,939	24,239	25,219
U.S. and Canada | Sublease income | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	10,508	11,087	31,982	34,485
U.S. and Canada | Cooperative advertising and other franchise support fees | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	4,558	4,739	14,379	16,245
U.S. and Canada | Other | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	28,007	31,700	84,777	96,543
International | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	36,940	51,407	117,311	140,107
International | Wholesale sales to franchisees | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	22,965	32,321	75,421	81,266
International | Royalties and franchise fees | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	6,792	7,150	19,111	20,347
International | Other | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	7,183	11,936	22,779	38,494
Manufacturing / Wholesale
Disaggregation of Revenue [Line Items]
Revenue	3,800		8,100
Manufacturing / Wholesale | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	17,402	115,954	106,080	352,901
Manufacturing / Wholesale | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	0	63,695	35,505	193,596
Manufacturing / Wholesale | Third-party contract manufacturing | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	0	31,212	15,783	94,514
Manufacturing / Wholesale | Intersegment sales | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue	0	63,695	35,505	193,596
Manufacturing / Wholesale | Wholesale partner sales | Operating Segment
Disaggregation of Revenue [Line Items]
Revenue	$ 17,402	$ 21,047	$ 54,792	$ 64,791