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Fair Value Measurements (Narrative) (Detail) (USD $)
Jun. 30, 2012
Dec. 31, 2011
Derivative liability, net $ 300,000 $ 300,000
Long-term debt 800,000,000 800,000,000
Long-term debt, fair value 806,000,000  
Asset retirement obligation, carrying value $ 17,260,000 $ 13,075,000