Value of Amortizable Intangible Assets (Detail) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 388,377	$ 318,344
Accumulated Amortization	35,630	28,394
Net Value	352,747	289,950
Covenants not-to-compete
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	10,855	10,402
Accumulated Amortization	3,712	2,952
Net Value	7,143	7,450
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	373,856	304,175
Accumulated Amortization	29,641	23,177
Net Value	344,215	280,998
Tradenames
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,200	1,200
Accumulated Amortization	269	253
Net Value	931	947
License agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	720	766
Accumulated Amortization	262	211
Net Value	458	555
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,746	1,801
Accumulated Amortization	1,746	1,801
Net Value	$ 0	$ 0