NATURE OF BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES (Risks and Uncertainties) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Revenues	$ 1,160,132	$ 914,128	$ 730,027
Customer Concentration Risk \| Sales Revenue, Net \| Top Five Customers
Concentration Risk [Line Items]
Concentration percentage	28.20%	32.60%	32.80%
Revenues	$ 327,092	$ 298,063	$ 239,396
Customer Concentration Risk \| Sales Revenue, Net \| Top Ten Customers
Concentration Risk [Line Items]
Concentration percentage	38.10%	43.80%	43.90%
Revenues	$ 442,253	$ 400,250	$ 320,126
CIS Countries \| Geographic Concentration Risk \| Assets, Total
Concentration Risk [Line Items]
Cash including time deposits and restricted cash	194,600
Belarus \| Geographic Concentration Risk \| Assets, Total
Concentration Risk [Line Items]
Cash including time deposits and restricted cash	$ 153,800

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
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