XML 159 R112.htm IDEA: XBRL DOCUMENT v3.8.0.1
Financial Risk Management - Summary of Hedge Positions (Detail)
$ / T in Thousands
 12 Months Ended
Dec. 31, 2017
$ / T
T
Lead 1 [member]  
Disclosure of detailed information about hedged items [line items]  
Hedged per Amount | T 7,668
Maturity Jan 2018 - Jun 2018
Lead 2 [member]  
Disclosure of detailed information about hedged items [line items]  
Hedged per Amount | T 7,668
Maturity Jul 2018 - Dec 2018
Zinc1 [member]  
Disclosure of detailed information about hedged items [line items]  
Hedged per Amount | T 12,708
Maturity Jan 2018 - Jun 2018
Zinc 2 [member]  
Disclosure of detailed information about hedged items [line items]  
Hedged per Amount | T 12,708
Maturity Jul 2018 - Dec 2018
PUT [member] | Lead 1 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 2,300
PUT [member] | Lead 2 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 2,300
PUT [member] | Zinc1 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 2,850
PUT [member] | Zinc 2 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 2,850
CALL [member] | Lead 1 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 2,625
CALL [member] | Lead 2 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 2,735
CALL [member] | Zinc1 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 3,470
CALL [member] | Zinc 2 [member]  
Disclosure of detailed information about hedged items [line items]  
Fair value hedges 3,600