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Asset Retirement Obligations - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]    
Accrued liability for AROs $ 340us-gaap_AssetRetirementObligationsNoncurrent $ 304us-gaap_AssetRetirementObligationsNoncurrent