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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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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Amount of interest capitalized during the period.

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-Name Accounting Standards Codification

-Glossary Allowance for Funds Used during Construction

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Represents the hypothetical financial impact of sustained price decrease over life of assets that would result in potential impairment, expressed as a percentage.

+ References

No definition available.

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Summary of Significant Accounting Policies (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, plant and equipment
Capitalized interest costs	$ 500,000us-gaap_InterestCostsCapitalized	$ 1,700,000us-gaap_InterestCostsCapitalized	$ 7,700,000us-gaap_InterestCostsCapitalized
Present values of the asset retirement obligations	112,327,000us-gaap_AssetRetirementObligation	116,393,000us-gaap_AssetRetirementObligation	89,478,000us-gaap_AssetRetirementObligation
Sustained price decrease over and above prices used in analysis through life of assets that would result in potential impairment as per sensitivity analysis (as a percent)	5.00%
Asset impairment charges	51,556,000us-gaap_AssetImpairmentCharges	0us-gaap_AssetImpairmentCharges	43,103,000us-gaap_AssetImpairmentCharges
Goodwill impairment	0us-gaap_GoodwillImpairmentLoss	0us-gaap_GoodwillImpairmentLoss	1,064,409,000us-gaap_GoodwillImpairmentLoss
BCCT
Property, plant and equipment
Asset impairment charges	51,600,000
North River Mine
Property, plant and equipment
Long-lived asset impairments	0
Asset impairment charges		$ 8,000,000
Machinery and equipment \| Minimum
Property, plant and equipment
Estimated useful lives	3 years
Machinery and equipment \| Maximum
Property, plant and equipment
Estimated useful lives	10 years
Land improvements and building \| Minimum
Property, plant and equipment
Estimated useful lives	15 years
Land improvements and building \| Maximum
Property, plant and equipment
Estimated useful lives	30 years
Capitalized computer systems and software implementation costs \| Minimum
Property, plant and equipment
Estimated useful lives	3 years
Capitalized computer systems and software implementation costs \| Maximum
Property, plant and equipment
Estimated useful lives	5 years