SEGMENT INFORMATION - Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment information
Operating income	$ 357,621	$ 350,041	$ 637,535	$ 614,303
Stock-based compensation expense	14,900	12,800	28,300	26,000
Corporate and unallocated
Segment information
Operating income	(68,099)	(61,075)	(133,460)	(119,766)
Payroll costs	44,700	38,400	87,800	76,100
Stock-based compensation expense	14,900	12,800	28,300	26,000
Professional service expenses	11,800	14,000	24,200	26,400
Other operating expenses	$ 11,600	$ 8,600	$ 21,400	$ 17,300