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Asset Retirement Obligations (Activity Associated With Asset Retirement Obligations) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Asset Retirement Obligations [Abstract]      
Asset retirement obligations, beginning of year $ 2,975 $ 3,031 $ 3,009
Liabilities incurred 100 0 2,000
Accretion expense 165 139 168
Liabilities settled 0 0 (1,539)
Changes in expected cash flows and timing 57 (195) (607)
Asset retirement obligations, end of year $ 3,297 $ 2,975 $ 3,031