XML 78 R64.htm IDEA: XBRL DOCUMENT v3.10.0.1
Asset Retirement Obligation - Reconciliation of Total Reclamation Liability for Asset Retirement Obligations (Detail)
$ in Thousands
9 Months Ended
Sep. 30, 2018
USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]  
December 31, 2017 $ 8,982
Additions and revisions of prior estimates 1,561
Accretion expense 330
Settlement of liability (2,219)
September 30, 2018 $ 8,654