Quarterly report pursuant to Section 13 or 15(d)

Asset Retirement Obligations (Details)

v3.10.0.1
Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Changes in asset retirement obligations        
Asset retirement obligations at beginning of period     $ 15,506 $ 14,200
Liabilities incurred     316 259
Liabilities settled     (1) (107)
Liabilities eliminated through asset sales     (8,699) (1,146)
Current period accretion expense $ 147 $ 274 694 833
Asset retirement obligations at end of period $ 7,816 $ 14,039 $ 7,816 $ 14,039