GOODWILL AND INTANGIBLE ASSETS - Components of intangible assets (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets	$ 297,155
Indefinite-lived intangible assets:	105,383
Total customer contracts and other intangible assets	402,538
Trademarks & Tradenames, Net
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets:	101,738
Total customer contracts and other intangible assets	108,200	$ 109,000
Internet domains
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets:	2,227
Other Intangible Assets, Net
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets:	1,418
Customer Contracts, Net
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets	$ 284,393	298,900
Customer Contracts, Net | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	3 years
Customer Contracts, Net | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	20 years
Trademarks & Tradenames, Net
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets	$ 6,493
Trademarks & Tradenames, Net | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	7 years
Trademarks & Tradenames, Net | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	20 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets	$ 4,316
Non-compete agreements | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	3 years
Non-compete agreements | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	20 years
Patents
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets	$ 1,441
Patents | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	3 years
Patents | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets useful life	15 years
Other Intangible Assets, Net
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets	$ 512
Total customer contracts and other intangible assets	$ 9,900	$ 10,800
Finite lived intangible assets useful life	10 years