CASH AND CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS; BANK OVERDRAFT (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended									6 Months Ended		12 Months Ended	6 Months Ended			12 Months Ended	6 Months Ended
	Jul. 31, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2013 Ruble-denominated deposits	Dec. 31, 2012 Ruble-denominated deposits	Jun. 30, 2013 US dollar-denominated deposits	Dec. 31, 2012 US dollar-denominated deposits	Jun. 30, 2013 Low end of range	Jun. 30, 2013 Low end of range Ruble-denominated deposits	Dec. 31, 2012 Low end of range Ruble-denominated deposits	Jun. 30, 2013 Low end of range US dollar-denominated deposits	Jun. 30, 2013 High end of range	Jun. 30, 2013 High end of range Ruble-denominated deposits	Dec. 31, 2012 High end of range Ruble-denominated deposits	Jun. 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						$ 13,037	$ 23,519	$ 10,195	$ 31,021
Other		1,341	641
Total cash and cash equivalents		24,573	55,181	25,808	12,331
Short-term investments		138,961	131,449			128,961	131,449	10,000
Annual interest rate (as a percent)											6.00%	7.65%	3.35%		9.00%	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		$ 17,291	$ 13,181