XML 108 R49.htm IDEA: XBRL DOCUMENT v2.4.0.6
Fair Value Measurements - Additional Information (Detail) (USD $)
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Derivative liability, net $ 29,000 $ 300,000  
Long-term debt 1,200,000,000 800,000,000  
Long-term debt, fair value 1,284,000,000    
Asset retirement obligation, carrying value $ 23,234,000 $ 13,075,000 $ 7,640,000