Quarterly report pursuant to Section 13 or 15(d)

Goodwill And Other Intangible Assets And Liabilities (Estimated Useful Lives Of Intangible Assets Subject To Periodic Amortization On A Straight-Line Basis) (Detail)

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Goodwill And Other Intangible Assets And Liabilities (Estimated Useful Lives Of Intangible Assets Subject To Periodic Amortization On A Straight-Line Basis) (Detail)
6 Months Ended
Jun. 30, 2012
Permits [Member] | Minimum [Member]
 
Finite-Lived Intangible Assets [Line Items]  
Intangible Assets Estimated Useful Life (years) 15 years
Permits [Member] | Maximum [Member]
 
Finite-Lived Intangible Assets [Line Items]  
Intangible Assets Estimated Useful Life (years) 28 years
Utility Contracts [Member]
 
Finite-Lived Intangible Assets [Line Items]  
Intangible Assets Estimated Useful Life (years) 5 years
Leases [Member] | Minimum [Member]
 
Finite-Lived Intangible Assets [Line Items]  
Intangible Assets Estimated Useful Life (years) 1 year 6 months
Leases [Member] | Maximum [Member]
 
Finite-Lived Intangible Assets [Line Items]  
Intangible Assets Estimated Useful Life (years) 4 years 6 months