Values of Intangible Assets (Detail) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	$ 563,108	$ 403,568
Accumulated Amortization	38,881	28,394
Net Value	524,227	375,174
Customer relationships | Amortizable intangibles
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	455,750	304,175
Accumulated Amortization	32,546	23,177
Net Value	423,204	280,998
Covenants not-to-compete | Amortizable intangibles
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	10,770	10,402
Accumulated Amortization	3,988	2,952
Net Value	6,782	7,450
Tradenames | Amortizable intangibles
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	2,556	1,200
Accumulated Amortization	360	253
Net Value	2,196	947
Amortizable intangibles | License agreements
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	720	766
Accumulated Amortization	288	211
Net Value	432	555
Amortizable intangibles | Other
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	1,699	1,801
Accumulated Amortization	1,699	1,801
Net Value	0	0
Operating permits | Indefinite lived intangibles
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	$ 91,613	$ 85,224