Derivative Financial Instruments - Summary of Mark-to-Market Gain (Losses) on Derivative Instruments (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) $ / oz	Mar. 31, 2017 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Fair value adjustments, net, pretax	$ 4,987,000	$ (1,200,000)
Fair value adjustments, net	$ 398,000	1,212,000
Zinc Put Options, Purchased [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Weighted Average Strike Price of Put Options | $ / oz	3,000.00
Provisional silver and gold sales contracts
Derivative Instruments, Gain (Loss) [Line Items]
Provisional gain (loss) on derivatives and commodity contracts	$ 253,000	1,212,000
Zinc options
Derivative Instruments, Gain (Loss) [Line Items]
Net derivative gain (loss)	100,000	$ 0
Derivative Asset	$ 145,000
Zinc Call Options, Sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Weighted Average Strike Price of Call Options	4,050