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Property And Equipment (Schedule Of Asset Retirement Obligation) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligation, beginning of period $ 13,275 $ 12,653  
Liabilities incurred 670 598  
Liabilities settled (780) (531)  
Accretion expense 175 176  
Asset retirement obligation as of end of period 13,340 12,896  
Less current portion 780 620 60
Asset retirement obligation, long-term $ 12,560 $ 12,276 $ 13,215