Quarterly report pursuant to Section 13 or 15(d)

Property and Equipment (Schedule of Asset Retirement Obligation) (Details)

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Property and Equipment (Schedule of Asset Retirement Obligation) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]          
Asset retirement obligation, beginning of period     $ 34,276 $ 26,437  
Liabilities incurred     9,505 3,195  
Liabilities settled     (344) (72)  
Accretion expense $ 410 $ 261 692 508  
Asset retirement obligation as of end of period 44,129 30,068 44,129 30,068  
Less current portion 195 75 195 75 $ 195
Asset retirement obligation, long-term $ 43,934 $ 29,993 $ 43,934 $ 29,993 $ 34,081