Derivative Financial Instruments - Narrative (Details) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 21, 2009 oz
Palmarejo gold production royalty
Derivative [Line Items]
Production to be sold, percent						50.00%
Payment made for gold on the end of royalty obligation | oz						4,167
Palmarejo gold production royalty | Maximum
Derivative [Line Items]
Payable ounces under royalty obligation | oz						400,000
Franco-Nevada warrant
Derivative [Line Items]
Market-to-market adjustment	$ 5,900	$ 17,000
Realized losses	$ 10,800	$ 13,900
Concentrate Sales Contracts
Derivative [Line Items]
Provisional gain (loss) on derivatives and commodity contracts			$ 631	$ (239)	$ 214
Silver and gold options
Derivative [Line Items]
Net derivative gain (loss)				$ 1,600	$ 1,300