Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Asset Retirement Obligations (Detail)

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Commitments and Contingencies - Asset Retirement Obligations (Detail) (USD $)
In Thousands, unless otherwise specified
9 Months Ended
Sep. 30, 2014
Asset Retirement Obligation Disclosure [Line Items]  
Beginning Balance $ 11,463
Accretion Expense 414
Additions 2,143
Settlements (361)
Ending Balance $ 13,659