SEGMENT INFORMATION - Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment information
Operating income	$ 279,915	$ 264,262
Stock-based compensation expense	13,400	13,100
Corporate and unallocated
Segment information
Operating income	(65,360)	(58,691)
Payroll costs	43,100	37,600
Stock-based compensation expense	13,400	13,100
Professional service expenses	12,400	12,300
Other operating expenses	$ 9,900	$ 8,800