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Accrued Liabilities - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Payables and Accruals [Abstract]    
Revenue suspense $ 79.7 $ 30.0
Production taxes payable 22.3 11.6
Royalties payable $ 44.7 $ 27.8