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Asset Retirement Obligations - Activity For Asset Retirement Obligations (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2015
USD ($)
Asset Retirement Obligation Disclosure [Abstract]  
Obligations assumed in business combination $ 6.5
Revisions and liabilities incurred (1.0)
Accretion expense 0.4
Payments (0.9)
Balance, December 31, 2015 $ 5.0