XML 102 R76.htm IDEA: XBRL DOCUMENT v3.10.0.1
Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligations (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset retirement obligation - beginning of period $ 48,799 $ 49,687
Liabilities incurred during period 5,854 2,449
Liabilities settled during period (4,944) (5,743)
Accretion expense during period 2,657 2,621
Revisions to estimates 83 (215)
Asset retirement obligation - end of period 52,449 48,799
Current portion of total ARO balance $ 100 $ 300