Quarterly report pursuant to Section 13 or 15(d)

Mineral Properties - rollforward (Details)

v3.7.0.1
Mineral Properties - rollforward (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Balance at beginning of period $ 47,029  
Increase in reclamation costs 614  
Change in estimated reclamation costs (Note 13) 613 $ (534)
Amortization (758)  
Balance at end of period 46,885 47,029
Lost Creek Property    
Balance at beginning of period 14,015  
Increase in reclamation costs 614  
Amortization (758)  
Balance at end of period 13,871 14,015
Path Finder Mines [Member]    
Balance at beginning of period 19,866  
Balance at end of period 19,866 19,866
Other U.S. Properties [Member]    
Balance at beginning of period 13,148  
Balance at end of period $ 13,148 $ 13,148