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Other Investments (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2015 USD ($)	Feb. 28, 2014 USD ($)	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) shares	Mar. 31, 2015 CAD / shares shares	Mar. 31, 2015 $ / shares shares	Feb. 28, 2014 CAD / shares shares	Feb. 28, 2014 $ / shares shares
Subsidiary, Sale of Stock [Line Items]
Unrealized loss on Midas Gold Shares			$ (624)	$ (3,792)	$ (1,326)	$ (2,370)
Realized gain on other investments, net (Note 2)					(348)	155
Proceeds from sale of other investments, net					2,772	10,560
Realized gain (loss) on other investments					(348)	155
Midas Gold Shares [Member]
Subsidiary, Sale of Stock [Line Items]
Number of shares sold \| shares								8,000,000	8,000,000	16,000,000	16,000,000
Sale of shares (dollars per share) \| (per share)								CAD 0.46	$ 0.36	CAD 0.80	$ 0.73
Realized gain on other investments, net (Note 2)	$ (348)					155
Proceeds from sale of other investments, net	$ 2,772	$ 10,560			$ 2,772		$ 10,560
Shares owned \| shares			7,802,615		7,802,615		15,802,615	7,802,615	7,802,615	15,802,615	15,802,615
Holding percentage	4.90%	11.20%			4.90%
Realized gain (loss) on other investments	$ (348)					$ 155