Derivative Financial Instruments - Summary of Provisionally Priced Sales $ in Thousands	Dec. 31, 2017 USD ($) oz $ / oz
Silver concentrate sales agreements | 2018
Derivative instruments Settlement
Derivative, notional amount | $	$ 383
Derivative average price | $ / oz	16.61
Outstanding Provisionally Priced Sales Consists of Silver | oz	23,065
Silver concentrate sales agreements | Thereafter
Derivative instruments Settlement
Derivative, notional amount | $	$ 0
Derivative average price | $ / oz	0.00
Outstanding Provisionally Priced Sales Consists of Silver | oz	0
Gold concentrates sales agreements | 2018
Derivative instruments Settlement
Derivative, notional amount | $	$ 53,214
Derivative average price | $ / oz	1,283.11
Outstanding Provisionally Priced Sales Consists of Gold | oz	41,476
Gold concentrates sales agreements | Thereafter
Derivative instruments Settlement
Derivative, notional amount | $	$ 0
Derivative average price | $ / oz	0.00
Outstanding Provisionally Priced Sales Consists of Gold | oz	0