XML 90 R59.htm IDEA: XBRL DOCUMENT v3.8.0.1
Decommissioning provision (Schedule of Decomissioning Provision) (Details) - Decommissioning Provision [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of other provisions [line items]    
Provisions, beginning of year $ 3,829 $ 4,568
Decommissioning costs and change in estimates (66) (891)
Accretion on decommissioning provision 185 152
Provisions, end of year $ 3,948 $ 3,829