GOODWILL AND INTANGIBLE ASSETS Goodwill (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Goodwill [Roll Forward]
Gross Balance, December 31, 2018	$ 1,138,945
Accumulated impairment losses, beginning balance	(462,612)
Balance, December 31, 2018	676,333
Foreign currency	(15,872)
Balance, March 31, 2019	660,461
Accumulated impairment losses, ending balance	(462,612)
Gross Balance, March 31, 2019	1,123,073
Bulgaria
Goodwill [Roll Forward]
Gross Balance, December 31, 2018	173,694
Accumulated impairment losses, beginning balance	(144,639)
Balance, December 31, 2018	29,055
Foreign currency	(545)
Balance, March 31, 2019	28,510
Accumulated impairment losses, ending balance	(144,639)
Gross Balance, March 31, 2019	173,149
Czech Republic
Goodwill [Roll Forward]
Gross Balance, December 31, 2018	808,970
Accumulated impairment losses, beginning balance	(287,545)
Balance, December 31, 2018	521,425
Foreign currency	(11,399)
Balance, March 31, 2019	510,026
Accumulated impairment losses, ending balance	(287,545)
Gross Balance, March 31, 2019	797,571
Romania
Goodwill [Roll Forward]
Gross Balance, December 31, 2018	86,800
Accumulated impairment losses, beginning balance	(11,028)
Balance, December 31, 2018	75,772
Foreign currency	(2,986)
Balance, March 31, 2019	72,786
Accumulated impairment losses, ending balance	(11,028)
Gross Balance, March 31, 2019	83,814
Slovak Republic
Goodwill [Roll Forward]
Gross Balance, December 31, 2018	50,081
Accumulated impairment losses, beginning balance	0
Balance, December 31, 2018	50,081
Foreign currency	(942)
Balance, March 31, 2019	49,139
Accumulated impairment losses, ending balance	0
Gross Balance, March 31, 2019	49,139
SLOVENIA
Goodwill [Roll Forward]
Gross Balance, December 31, 2018	19,400
Accumulated impairment losses, beginning balance	(19,400)
Balance, December 31, 2018	0
Foreign currency	0
Balance, March 31, 2019	0
Accumulated impairment losses, ending balance	(19,400)
Gross Balance, March 31, 2019	$ 19,400