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Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Sep. 30, 2011
Dec. 31, 2010
Debt Disclosure [Abstract]        
Asset retirement obligation (ARO) liability $ 144,849 $ 96,446 $ 92,802 $ 69,265
Workers' compensation 17,267 17,026    
Separation benefit plans 7,484 6,845    
Gas balancing liability 3,263 3,263    
Deferred compensation plan 2,720 2,463    
Other liabilities 175,583 126,043    
Less current portion 11,413 12,213    
Total other long-term liabilities $ 164,170 $ 113,830