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Derivative Financial Instruments - Summary of Mark-to-Market Gain (Losses) on Derivative Instruments (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]        
Fair value adjustments, net, pretax $ 4,377 $ 715 $ 8,201 $ 2,907
Fair value adjustments, net 248 465 (1,634) 621
Provisional metal sales contracts        
Derivative Instruments, Gain (Loss) [Line Items]        
Provisional gain (loss) on derivatives and commodity contracts 233 34 (1,461) 15
Zinc options        
Derivative Instruments, Gain (Loss) [Line Items]        
Net derivative gain (loss) 0 225 0  
Interest rate swap        
Derivative Instruments, Gain (Loss) [Line Items]        
Net derivative gain (loss) $ 15 $ 206 $ (173) $ 18