Summary of Significant Accounting Policies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Dec. 31, 2016	Oct. 02, 2014
Business Acquisition [Line Items]
Aggregate deposit to be received					$ 20,000,000.0
Production to be sold, percent					50.00%
Price per ounce under agreement					$ 800
Adoption of new accounting standard	$ 65,000,000.0
Drilling and Related Costs Capitalized	7,500,000	$ 18,600,000
Impairment of long-lived assets	250,814,000	0	$ 0
Write-downs	43,600,000	201,500,000	5,700,000
Revenue liability	11,061,000	12,918,000	$ 14,883,000		$ 19,281,000
Debt Securities, Held-to-maturity, Restricted	8,800,000	12,300,000
Restricted Cash Equivalents	$ 1,373,000	$ 2,988,000
Palmarejo gold production royalty
Business Acquisition [Line Items]
Aggregate deposit to be received						$ 22,000,000.0
Production to be sold, percent						50.00%
Price per ounce under agreement						$ 800
Building and Building Improvements | Minimum
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Building and Building Improvements | Maximum
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	30 years
Machinery and Equipment | Minimum
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Machinery and Equipment | Maximum
Business Acquisition [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Kensington
Business Acquisition [Line Items]
Revenue liability	$ 15,000,000.0			$ 25,000,000.0