Geographic Information for Revenue Earned (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, Revenue Reconciling Item [Line Items]
Revenues	$ 124,716	$ 114,341	$ 104,407	$ 106,394	$ 120,141	$ 105,563	$ 95,737	$ 100,869	$ 449,858		$ 422,310		$ 395,379
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									444,074		416,154		390,424
International
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									$ 5,784	[1]	$ 6,156	[1]	$ 4,955	[1]

[1] The revenues of the individual countries comprising these amounts are not significant.