SEGMENT INFORMATION - Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment information
Operating income	$ 311,461	$ 279,915
Stock-based compensation expense	15,300	13,400
Corporate and unallocated
Segment information
Operating income	(78,021)	(65,360)
Payroll costs	50,400	43,100
Stock-based compensation expense	15,300	13,400
Professional service expenses	17,500	12,400
Other operating expenses	$ 10,100	$ 9,900