SEGMENTS INFORMATION - Revenues from External Customers and Operating Profit/(Loss) Before Unallocated Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 348,977	$ 283,832	$ 673,628	$ 548,314
Operating profit	40,682	32,080	71,648	62,411
Russia
Segment Reporting Information [Line Items]
Revenues	13,326	10,505	26,535	19,470
Operating Segments
Segment Reporting Information [Line Items]
Revenues	349,021	283,977	673,724	548,791
Operating profit	66,175	54,628	126,627	103,275
Operating Segments | North America
Segment Reporting Information [Line Items]
Revenues	194,025	157,110	372,328	304,600
Operating profit	43,622	38,339	80,714	68,994
Operating Segments | Europe
Segment Reporting Information [Line Items]
Revenues	141,319	115,726	274,026	223,569
Operating profit	20,658	13,413	40,469	30,245
Operating Segments | Russia
Segment Reporting Information [Line Items]
Revenues	13,677	11,141	27,370	20,622
Operating profit	$ 1,895	$ 2,876	$ 5,444	$ 4,036