XML 70 R59.htm IDEA: XBRL DOCUMENT v3.19.2
Fixed Assets, Mineral Leaseholds, and Asset Retirement Obligations (Asset Retirement Obligation Rollforward) (Details)
$ in Thousands
6 Months Ended
Jun. 30, 2019
USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]  
ARO liability balance, December 31, 2018 $ 239,865
Accretion expense 4,576
Changes in estimate (15,711)
Settlements (20,277)
ARO liability balance, June 30, 2019 $ 208,453