CASH AND CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS; BANK OVERDRAFT (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended									9 Months Ended		12 Months Ended	9 Months Ended			12 Months Ended	9 Months Ended
	Jul. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2013 Ruble-denominated deposits	Dec. 31, 2012 Ruble-denominated deposits	Sep. 30, 2013 US dollar-denominated deposits	Dec. 31, 2012 US dollar-denominated deposits	Sep. 30, 2013 Low end of range	Sep. 30, 2013 Low end of range Ruble-denominated deposits	Dec. 31, 2012 Low end of range Ruble-denominated deposits	Sep. 30, 2013 Low end of range US dollar-denominated deposits	Sep. 30, 2013 High end of range	Sep. 30, 2013 High end of range Ruble-denominated deposits	Dec. 31, 2012 High end of range Ruble-denominated deposits	Sep. 30, 2013 High end of range US dollar-denominated deposits
CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS; BANK OVERDRAFT
Deposits in banks with original maturity period for classification as short-term investments										91 days				365 days
Bank accounts						$ 23,896	$ 23,519	$ 2,698	$ 31,021
Other		1,180	641
Total cash and cash equivalents		27,774	55,181	24,001	12,331
Short-term investments		99,169	131,449			89,169	131,449	10,000
Annual interest rate (as a percent)											6.50%	7.65%	3.35%		8.75%	9.25%	3.52%
Variable interest rate basis	Mosprime rate
Variable interest rate (as a percent)	2.21%
Credit limit under overdraft agreement	31,000
Overdraft position		$ 4,270	$ 13,181