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Fair Value Accounting (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value Transfers Between Levels $ 0  
Recurring [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 88 $ 109
Other investments (Midas Gold Shares) 4,136 4,994
Recurring [Member] | Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 88 109
Other investments (Midas Gold Shares) $ 4,136 4,994
Non-recurring [Member] | Used mill equipment, Canada [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equipment   6,500
Non-recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Used mill equipment, Canada [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equipment   $ 6,500