Georgraphic Information for Revenues (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues:
Revenues	$ 158,123	$ 167,083	$ 149,669	$ 150,830	$ 119,584	$ 118,517	$ 111,532	$ 123,449	$ 625,705	$ 473,082	$ 341,872
UNITED STATES
Revenues:
Revenues									495,777	365,346	258,453
CANADA
Revenues:
Revenues									34,001	28,926	22,062
Other International
Revenues:
Revenues									$ 95,927	$ 78,810	$ 61,357