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Fair Value Measurements - Additional Information (Detail) (USD $)
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Fair Value Disclosures [Abstract]      
Derivative liability, net $ 200,000 $ 29,000  
Asset retirement obligation, carrying value 36,458,000 23,234,000 13,075,000
Debt Instrument [Line Items]      
Long-term debt, carrying value 2,535,570,000 1,200,000,000  
Senior unsecured notes [Member]
     
Debt Instrument [Line Items]      
Long-term, unsecured notes and borrowings 2,200,000,000    
Long-term debt, fair value 2,344,000,000    
Amended Credit Facility [Member]
     
Debt Instrument [Line Items]      
Long-term, unsecured notes and borrowings $ 335,600,000