Derivative Financial Instruments - Summary of Classification of Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Prepaid expenses and other
Fair value of the derivative instruments
Other derivative instruments, net	$ 717
Accrued liabilities and other
Fair value of the derivative instruments
Fair value of derivative liability	267
Non-current portion of royalty obligation
Fair value of the derivative instruments
Fair value of derivative liability	0
Silver and Gold Concentrate Sales Agreements | Prepaid expenses and other
Fair value of the derivative instruments
Other derivative instruments, net	310	$ 251
Silver and Gold Concentrate Sales Agreements | Accrued liabilities and other
Fair value of the derivative instruments
Fair value of derivative liability	267	222
Silver and Gold Concentrate Sales Agreements | Non-current portion of royalty obligation
Fair value of the derivative instruments
Fair value of derivative liability	0	$ 0
Zinc Put and Call Options [Member] | Prepaid expenses and other
Fair value of the derivative instruments
Other derivative instruments, net	339
Zinc Put and Call Options [Member] | Non-current portion of royalty obligation
Fair value of the derivative instruments
Fair value of derivative liability	0
Interest rate swap | Prepaid expenses and other
Fair value of the derivative instruments
Other derivative instruments, net	68
Interest rate swap | Non-current portion of royalty obligation
Fair value of the derivative instruments
Fair value of derivative liability	$ 0