CASH AND CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS; OTHER NON-CURRENT ASSETS (Details) (USD $) In Thousands, unless otherwise specified							12 Months Ended		3 Months Ended		12 Months Ended	3 Months Ended			12 Months Ended	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2014 Ruble-denominated deposits	Dec. 31, 2013 Ruble-denominated deposits	Dec. 31, 2013 US dollar-denominated deposits	Mar. 31, 2014 US dollar-denominated deposits	Mar. 31, 2014 Low end of range	Mar. 31, 2014 Low end of range Ruble-denominated deposits	Dec. 31, 2013 Low end of range Ruble-denominated deposits	Mar. 31, 2014 Low end of range US dollar-denominated deposits	Mar. 31, 2014 High end of range	Mar. 31, 2014 High end of range Ruble-denominated deposits	Dec. 31, 2013 High end of range Ruble-denominated deposits	Mar. 31, 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					$ 21,363	$ 16,616	$ 12,754	$ 12,916
Other	3,460	1,204
Total cash and cash equivalents	37,739	30,574	15,400	55,181
Short-term investments	$ 160,663	$ 180,337			$ 130,663	$ 178,937	$ 1,400	$ 30,000
Annual interest rate (as a percent)							0.27%			7.00%	6.30%	0.75%		9.00%	9.00%	1.40%