Summary of Purchased Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	9 Months Ended	12 Months Ended
	Aug. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Aug. 20, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned				$ 57,720
Weighted Average Amortization Period (years)	8 years	8 years	8 years
Customer relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned				46,000
Weighted Average Amortization Period (years)	8 years	8 years	8 years
Trade names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned				10,600
Weighted Average Amortization Period (years)	8 years	8 years	3 years
Non-compete agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned				670
Weighted Average Amortization Period (years)	2 years	2 years	1 year
Favorable Lease Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Amount Assigned				$ 450
Weighted Average Amortization Period (years)	2 years	2 years