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Asset Retirement Obligations (Components Of Changes In Asset Retirement Obligation Liability) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Asset Retirement Obligations [Abstract]    
Asset retirement obligation, January 1 $ 4,884 $ 4,521
Accretion expense 211 363
Payments     
Asset retirement obligation, December 31 $ 5,095 $ 4,884