CASH AND CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS; OTHER NON-CURRENT ASSETS (Details) (USD $) In Thousands, unless otherwise specified							12 Months Ended		9 Months Ended		12 Months Ended	9 Months Ended			12 Months Ended	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2014 Ruble-denominated deposits	Dec. 31, 2013 Ruble-denominated deposits	Dec. 31, 2013 US dollar-denominated deposits	Sep. 30, 2014 US dollar-denominated deposits	Sep. 30, 2014 Low end of range	Sep. 30, 2014 Low end of range Ruble-denominated deposits	Dec. 31, 2013 Low end of range Ruble-denominated deposits	Sep. 30, 2014 Low end of range US dollar-denominated deposits	Sep. 30, 2014 High end of range	Sep. 30, 2014 High end of range Ruble-denominated deposits	Dec. 31, 2013 High end of range Ruble-denominated deposits	Sep. 30, 2014 High end of range US dollar-denominated deposits
CASH AND CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS; OTHER NON-CURRENT ASSETS
Deposits in banks with original maturity period for classification as short-term investments									91 days				365 days
Bank accounts					$ 11,779	$ 16,616	$ 12,754	$ 15,718
Other	2,340	1,204
Total cash and cash equivalents	29,837	30,574	27,774	55,181
Short-term investments	$ 121,982	$ 180,337			$ 72,982	$ 178,937	$ 1,400	$ 49,000
Annual interest rate (as a percent)							0.27%			7.00%	6.30%	0.74%		9.00%	9.00%	2.57%