Quarterly report pursuant to Section 13 or 15(d)

Mineral Properties - rollforward (Details)

v3.8.0.1
Mineral Properties - rollforward (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Balance at beginning of period $ 44,677  
Acquisition costs 14  
Change in estimated reclamation costs (Note 13)   $ 448
Amortization (435)  
Balance at end of period 44,256 44,677
Lost Creek Property    
Balance at beginning of period 11,810  
Amortization (435)  
Balance at end of period 11,375 11,810
Path Finder Mines [Member]    
Balance at beginning of period 19,701  
Balance at end of period 19,701 19,701
Other U.S. Properties [Member]    
Balance at beginning of period 13,166  
Acquisition costs 14  
Balance at end of period $ 13,180 $ 13,166