XML 81 R67.htm IDEA: XBRL DOCUMENT v3.19.1
Derivative Financial Instruments - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Concentrate Sales Contracts    
Derivative [Line Items]    
Provisional gain (loss) on derivatives and commodity contracts $ 250 $ 253
Zinc options    
Derivative [Line Items]    
Net derivative gain (loss) $ 0 145
Interest rate swap    
Derivative [Line Items]    
Term of contract 12 months  
Net derivative gain (loss) $ (46) $ 0