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Short-term and Other Investments, Summary (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Gain/(loss) during the period $ (312) $ 543  
Midas Gold Shares [Member]      
Fair value at beginning of period 4,994 $ 1,798 $ 1,798
Gain/(loss) during the period (312)   3,196
Fair value at end of period $ 4,682   $ 4,994
Midas Gold Shares held at end of the period 7,802,615   7,802,615