Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
Property and Equipment - Schedule of Asset Retirement Obligation (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligation, beginning of period $ 34,276 $ 26,437  
Liabilities incurred 42,270 10,971 $ 8,800
Liabilities settled (3,057) (4,189)  
Accretion expense 1,611 1,057 820
Revisions in estimated cash flows   0  
Asset retirement obligation as of end of period 75,100 34,276 $ 26,437
Less current portion 120 195  
Asset retirement obligation, long-term $ 74,980 $ 34,081