GOODWILL AND INTANGIBLE ASSETS - Definite Lived Intangibles (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Intangible assets with definite lives
Cost	$ 225,400	$ 261,705
Accumulated Amortization	(107,040)	(90,267)
Net	118,360	171,438
Technology
Intangible assets with definite lives
Cost	87,700	116,200
Accumulated Amortization	(48,166)	(48,938)
Net	$ 39,534	$ 67,262
Technology | Weighted Average
Intangible assets with definite lives
Weighted Average Amortization Life	4 years 3 months 18 days	4 years 2 months 12 days
Customer lists
Intangible assets with definite lives
Cost	$ 77,300	$ 77,300
Accumulated Amortization	(18,560)	(12,452)
Net	$ 58,740	$ 64,848
Customer lists | Weighted Average
Intangible assets with definite lives
Weighted Average Amortization Life	13 years 2 months 12 days	13 years 2 months 12 days
Trademarks and trade names
Intangible assets with definite lives
Cost	$ 17,200	$ 17,200
Accumulated Amortization	(9,947)	(6,407)
Net	$ 7,253	$ 10,793
Trademarks and trade names | Weighted Average
Intangible assets with definite lives
Weighted Average Amortization Life	4 years 10 months 24 days	4 years 10 months 24 days
Website content
Intangible assets with definite lives
Cost	$ 43,200	$ 51,000
Accumulated Amortization	(30,367)	(22,467)
Net	$ 12,833	$ 28,533
Website content | Weighted Average
Intangible assets with definite lives
Weighted Average Amortization Life	3 years	3 years
Other
Intangible assets with definite lives
Cost		$ 5
Accumulated Amortization		(3)
Net		$ 2
Other | Weighted Average
Intangible assets with definite lives
Weighted Average Amortization Life		3 years