SEGMENT INFORMATION - Revenue and Long-Lived Assets by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Revenue and Long-lived Assets by Geography
Revenue	$ 387,029	$ 343,650
Long-lived assets (excluding goodwill and intangible assets):	111,431		$ 108,842
United States
Revenue and Long-lived Assets by Geography
Revenue	356,444	319,821
Long-lived assets (excluding goodwill and intangible assets):	101,151		97,841
All other countries
Revenue and Long-lived Assets by Geography
Revenue	30,585	$ 23,829
Long-lived assets (excluding goodwill and intangible assets):	$ 10,280		$ 11,001