Values of Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	$ 681,273	$ 588,668
Accumulated Amortization	57,855	42,050
Net Value	623,418	546,618
Amortizable intangibles | Covenants not-to-compete
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	10,978	10,903
Accumulated Amortization	5,496	4,350
Net Value	5,482	6,553
Amortizable intangibles | Customer relationships
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	550,045	480,033
Accumulated Amortization	51,288	36,994
Net Value	498,757	443,039
Amortizable intangibles | Tradenames
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	4,919	2,556
Accumulated Amortization	675	391
Net Value	4,244	2,165
Amortizable intangibles | License agreements
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	720	720
Accumulated Amortization	394	315
Net Value	326	405
Amortizable intangibles | Other Intangible Assets
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	89	0
Accumulated Amortization	2	0
Net Value	87	0
Indefinite lived intangibles | Operating permits
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	114,522	94,456
Accumulated Amortization	0	0
Net Value	$ 114,522	$ 94,456