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Property And Equipment (Schedule Of Asset Retirement Obligation) (Details) (USD $)
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Dec. 31, 2011
Property And Equipment [Abstract]      
Asset retirement obligation, beginning of period $ 12,653,000 $ 10,845,000  
Liabilities incurred 598,000 174,000  
Liabilities settled (531,000)    
Accretion expense 176,000 159,000  
Asset retirement obligation as of end of period 12,896,000 11,178,000  
Less current portion 620,000 635,000 620,000
Asset retirement obligation, long-term $ 12,276,000 $ 10,543,000 $ 12,033,000