SEGMENT INFORMATION - Revenue and Long-Lived Assets by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenue and Long-lived Assets by Geography
Revenue	$ 343,650	$ 303,443
Long-lived assets (excluding goodwill, intangible assets and ROU assets)	103,806		$ 103,361
United States
Revenue and Long-lived Assets by Geography
Revenue	319,821	278,478
Long-lived assets (excluding goodwill, intangible assets and ROU assets)	95,623		95,822
All other countries
Revenue and Long-lived Assets by Geography
Revenue	23,829	$ 24,965
Long-lived assets (excluding goodwill, intangible assets and ROU assets)	$ 8,183		$ 7,539