GOODWILL AND INTANGIBLE ASSETS Goodwill (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Gross Balance, December 31, 2017	$ 1,155,571
Accumulated impairment losses, beginning balance	(443,212)
Balance, December 31, 2017	712,359
Foreign currency	21,863
Balance, March 31, 2018	734,222
Accumulated impairment losses, ending balance	(443,212)
Gross Balance, March 31, 2018	1,177,434
Bulgaria
Goodwill [Roll Forward]
Gross Balance, December 31, 2017	175,071
Accumulated impairment losses, beginning balance	(144,639)
Balance, December 31, 2017	30,432
Foreign currency	832
Balance, March 31, 2018	31,264
Accumulated impairment losses, ending balance	(144,639)
Gross Balance, March 31, 2018	175,903
Czech Republic
Goodwill [Roll Forward]
Gross Balance, December 31, 2017	837,732
Accumulated impairment losses, beginning balance	(287,545)
Balance, December 31, 2017	550,187
Foreign currency	17,321
Balance, March 31, 2018	567,508
Accumulated impairment losses, ending balance	(287,545)
Gross Balance, March 31, 2018	855,053
Romania
Goodwill [Roll Forward]
Gross Balance, December 31, 2017	90,305
Accumulated impairment losses, beginning balance	(11,028)
Balance, December 31, 2017	79,277
Foreign currency	2,271
Balance, March 31, 2018	81,548
Accumulated impairment losses, ending balance	(11,028)
Gross Balance, March 31, 2018	92,576
Slovak Republic
Goodwill [Roll Forward]
Gross Balance, December 31, 2017	52,463
Accumulated impairment losses, beginning balance	0
Balance, December 31, 2017	52,463
Foreign currency	1,439
Balance, March 31, 2018	53,902
Accumulated impairment losses, ending balance	0
Gross Balance, March 31, 2018	$ 53,902