XML 173 R159.htm IDEA: XBRL DOCUMENT v3.21.1
Financial Risk Management Objectives - Commodity Price Sensitivity (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
16% increase in commodity price [Member]    
Disclosure of nature and extent of risks arising from financial instruments [Line Items]    
Percentage of change of commodity price 28.00% (16.00%)
Effect on profit before tax due to change in commodity price $ 5,398 $ (3,473)
16% decrease in commodity price [Member]    
Disclosure of nature and extent of risks arising from financial instruments [Line Items]    
Percentage of change of commodity price (28.00%) 16.00%
Effect on profit before tax due to change in commodity price $ (5,398) $ 3,473