SEGMENT INFORMATION - Geographic Information about Revenue and Long-Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenue and long-lived assets by geography
Revenue	$ 1,105,843	$ 995,075
Property and equipment, net of accumulated depreciation and amortization	325,888		$ 318,800
United States
Revenue and long-lived assets by geography
Revenue	712,381	657,580
Property and equipment, net of accumulated depreciation and amortization	298,534		289,756
All other countries
Revenue and long-lived assets by geography
Revenue	393,462	$ 337,495
Property and equipment, net of accumulated depreciation and amortization	$ 27,354		$ 29,044