Revenues from External Customers and Segment Operating Profit before Unallocated Expenses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 125,538	$ 110,078	$ 103,800	$ 94,383	$ 95,127	$ 86,423	$ 80,176	$ 72,802	$ 433,799	$ 334,528	$ 221,824
Operating profit	18,656	16,736	16,830	13,784	15,427	16,891	10,878	11,812	66,006	55,008	32,790
Russia
Segment Reporting Information [Line Items]
Revenues									47,507	43,799	31,488
Operating Segments
Segment Reporting Information [Line Items]
Revenues									433,722	334,287	221,509
Operating profit									87,455	71,703	48,086
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues									16,986	12,851	11,522
Operating profit									6,985	2,416	1,414
Operating Segments | North America
Segment Reporting Information [Line Items]
Revenues									197,271	151,707	110,179
Operating profit									38,671	33,744	28,496
Operating Segments | EU
Segment Reporting Information [Line Items]
Revenues									168,913	123,510	68,420
Operating profit									32,750	25,098	15,057
Operating Segments | Russia
Segment Reporting Information [Line Items]
Revenues									50,552	46,219	31,388
Operating profit									$ 9,049	$ 10,445	$ 3,119