Annual report pursuant to Section 13 and 15(d)

Restricted Cash (Details)

v3.8.0.1
Restricted Cash (Details) - USD ($)
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Restricted Cash      
Restricted cash $ 7,558,000 $ 7,557,000 $ 7,557,000
Reclamation bonding requirement 27,081,000    
Certificate of deposit [Member]      
Restricted Cash      
Restricted cash 100,000 100,000  
Money Market Funds [Member]      
Restricted Cash      
Restricted cash 7,458,000 $ 7,457,000  
Money Market Funds [Member] | Surety Bond [Member]      
Restricted Cash      
Restricted cash pledged as collateral $ 7,444,000