Annual report pursuant to Section 13 and 15(d)

财产及设备（资产退休义务表）（详情）

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财产和设备（资产退休义务表）（详细信息）（美元）
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
资产退休义务，前滚分析[前滚]      
Asset retirement obligation, beginning of period $ 12,653 $ 10,845  
Liabilities incurred 2,195 1,390 1,328
Liabilities settled (2,271) (248)  
Accretion expense 698 666 617
Asset retirement obligation as of end of period 13,275 12,653 10,845
Less current portion 60 620  
Asset retirement obligation, long-term $ 13,215 $ 12,033