GOODWILL AND INTANGIBLE ASSETS Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 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	(35,906)
Balance, September 30, 2019	640,427
Accumulated impairment losses, ending balance	(462,612)
Gross Balance, September 30, 2019	1,103,039
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	(1,423)
Balance, September 30, 2019	27,632
Accumulated impairment losses, ending balance	(144,639)
Gross Balance, September 30, 2019	172,271
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	(27,295)
Balance, September 30, 2019	494,130
Accumulated impairment losses, ending balance	(287,545)
Gross Balance, September 30, 2019	781,675
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	(4,729)
Balance, September 30, 2019	71,043
Accumulated impairment losses, ending balance	(11,028)
Gross Balance, September 30, 2019	82,071
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	(2,459)
Balance, September 30, 2019	47,622
Accumulated impairment losses, ending balance	0
Gross Balance, September 30, 2019	47,622
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, September 30, 2019	0
Accumulated impairment losses, ending balance	(19,400)
Gross Balance, September 30, 2019	$ 19,400