Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Carrying amount of assets sold under agreements to repurchase when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under repurchase agreements exceeds 10 percent of total assets.

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Mineral properties, net of adjustments.

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This describes the time frame of the terms of the entity's repurchase agreements.

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Amount of cash inflow after closing and debt issuance costs received by a seller-lessee in a sale-leaseback recognized in financing activities.

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Asset Impairment Review (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Impairment Effects on Earnings Per Share [Line Items]
Asset impairment			$ 16,560
Proceeds from bulldog property		$ 4,940
Property, Plant and Equipment [Member]
Impairment Effects on Earnings Per Share [Line Items]
Asset impairment			15,100
Carlisle Assets [Member]
Impairment Effects on Earnings Per Share [Line Items]
Mine carring value			110,000
Asset impairment			$ 1,500
Bulldog Mine [Member]
Impairment Effects on Earnings Per Share [Line Items]
Proceeds from bulldog property	$ 4,900
Period of rights to repurchase the property		8 years
Assets with repurchase agreement aggregate net carrying value		$ 15,000