Asset Impairment Review (Narrative) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($)
Impairment Effects on Earnings Per Share [Line Items]
Asset impairment charge	$ 16,560
Property, Plant and Equipment [Member]
Impairment Effects on Earnings Per Share [Line Items]
Asset impairment charge	15,100
Carlisle Assets [Member]
Impairment Effects on Earnings Per Share [Line Items]
Mine carring value	118,000
Asset impairment charge	$ 1,500

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=51824106&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration