SEGMENT INFORMATION - Revenue and Long-Lived Assets by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue and Long-lived Assets by Geography
Revenue:	$ 389,913	$ 357,358	$ 1,108,624	$ 1,004,697
Long-lived assets (excluding goodwill, intangible assets and ROU assets):	104,323		104,323		$ 103,361
United States
Revenue and Long-lived Assets by Geography
Revenue:	368,082	335,230	1,041,903	934,409
Long-lived assets (excluding goodwill, intangible assets and ROU assets):	94,341		94,341		95,822
All other countries
Revenue and Long-lived Assets by Geography
Revenue:	21,831	$ 22,128	66,721	$ 70,288
Long-lived assets (excluding goodwill, intangible assets and ROU assets):	$ 9,982		$ 9,982		$ 7,539