Quarterly report pursuant to Section 13 or 15(d)

Mineral Properties - rollforward (Details)

v3.7.0.1
Mineral Properties - rollforward (Details) - USD ($)
$ in Thousands
 6 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Balance at beginning of period $ 47,029  
Increase in reclamation costs 816  
Change in estimated reclamation costs (Note 13) 815 $ (534)
Amortization (1,515)  
Balance at end of period 46,336 47,029
Lost Creek Property    
Balance at beginning of period 14,016  
Increase in reclamation costs 614  
Amortization (1,515)  
Balance at end of period 13,115 14,016
Path Finder Mines [Member]    
Balance at beginning of period 19,866  
Increase in reclamation costs 202  
Balance at end of period 20,068 19,866
Other U.S. Properties [Member]    
Balance at beginning of period 13,147  
Balance at end of period $ 13,153 $ 13,147