SEGMENT INFORMATION - Revenue and Long-Lived Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue and Long-lived Assets by Geography
Revenue	$ 4,262,892	$ 3,307,239	$ 3,139,882
Long-lived assets (excluding goodwill and intangible assets)	318,800	315,170
United States
Revenue and Long-lived Assets by Geography
Revenue	2,824,928	2,323,050	2,318,976
Long-lived assets (excluding goodwill and intangible assets)	289,756	286,541
All other countries
Revenue and Long-lived Assets by Geography
Revenue	1,437,964	984,189	$ 820,906
Long-lived assets (excluding goodwill and intangible assets)	$ 29,044	$ 28,629