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Accrued Final Capping, Closure and Post Closure - Changes to Accrued Capping, Closure and Post-Closure Liabilities (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]    
Beginning balance $ 39,829us-gaap_AssetRetirementObligation $ 46,326us-gaap_AssetRetirementObligation
Obligations incurred 441us-gaap_AssetRetirementObligationLiabilitiesIncurred 736us-gaap_AssetRetirementObligationLiabilitiesIncurred
Accretion expense 828us-gaap_AssetRetirementObligationAccretionExpense 983us-gaap_AssetRetirementObligationAccretionExpense
Obligations settled (504)us-gaap_AssetRetirementObligationLiabilitiesSettled (212)us-gaap_AssetRetirementObligationLiabilitiesSettled
Ending balance $ 40,594us-gaap_AssetRetirementObligation $ 47,833us-gaap_AssetRetirementObligation