Impairment Or Impairment Reversal of Mineral Properties and Other Assets - Additional Information (Details)	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / Ounce
Disclosure Of Impairment Loss And Reversal Of Impairment Loss [Abstract]
Impairment or reversal of impairment	$ 0
Recognized impairment reversal		$ 23,699,000
Fair value assumption of assets \| $ / Ounce		1,250
Discount rate of forecast asset		6.00%

Key economic assumptions included in valuation assessment.

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- Definition

The discount rate applied to cash flow projections for a cash-generating unit (group of units). [Refer: Cash-generating units [member]]

+ References

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- Definition

The amount of impairment loss or reversal of impairment loss recognised in profit or loss. [Refer: Impairment loss recognised in profit or loss; Reversal of impairment loss recognised in profit or loss]

+ References

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- Definition

The amount of reversal of impairment loss recognised in profit or loss. [Refer: Reversal of impairment loss; Profit (loss)]

+ References

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