Values of Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	$ 588,668	$ 403,568
Accumulated Amortization	42,050	28,394
Net Carrying Amount	546,618	375,174
Amortizable intangibles | Covenants not-to-compete
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	10,903	10,402
Accumulated Amortization	4,350	2,952
Net Carrying Amount	6,553	7,450
Amortizable intangibles | Customer relationships
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	480,033	304,175
Accumulated Amortization	36,994	23,177
Net Carrying Amount	443,039	280,998
Amortizable intangibles | Tradenames
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	2,556	1,200
Accumulated Amortization	391	253
Net Carrying Amount	2,165	947
Amortizable intangibles | License agreements
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	720	766
Accumulated Amortization	315	211
Net Carrying Amount	405	555
Amortizable intangibles | Other
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	0	1,801
Accumulated Amortization	0	1,801
Net Carrying Amount	0	0
Indefinite lived intangibles | Operating permits
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	94,456	85,224
Accumulated Amortization	0	0
Net Carrying Amount	$ 94,456	$ 85,224