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Short-term and Other Investments, Summary (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Fair value at beginning of period			$ 3,746
Gain (loss) during the period	$ (274)	$ (78)	1,754	$ (858)
Fair value at end of period	5,500		5,500		$ 3,746
Midas Gold Shares [Member]
Debt and Equity Securities, FV-NI [Line Items]
Fair value at beginning of period			3,746	$ 4,994	4,994
Gain (loss) during the period			1,754		(1,248)
Fair value at end of period	$ 5,500		$ 5,500		$ 3,746
Midas Gold Shares held at end of the period	7,802,615		7,802,615		7,802,615

X

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

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Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

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