SEGMENT INFORMATION - Revenue and Long-Lived Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue and Long-lived Assets by Geography
Revenue	$ 1,685,438	$ 1,467,925	$ 1,326,205
Long-lived assets (excluding goodwill and intangible assets)	118,267	108,842
United States
Revenue and Long-lived Assets by Geography
Revenue	1,581,051	1,379,236	$ 1,234,755
Long-lived assets (excluding goodwill and intangible assets)	$ 111,136	$ 97,841
United States | Revenue Benchmark | Geographic Concentration Risk
Revenue and Long-lived Assets by Geography
Revenue concentration risk percentage (greater than)	10.00%	10.00%	10.00%
All other countries
Revenue and Long-lived Assets by Geography
Revenue	$ 104,387	$ 88,689	$ 91,450
Long-lived assets (excluding goodwill and intangible assets)	$ 7,131	$ 11,001