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 aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale.

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The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan and expenses resulting from the write-down of assets. Excludes expenses related to a business combination, a discontinued operation or an asset retirement obligation.

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Costs related to the impairment of oil and gas properties.

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Represents the gain (loss) related to the release of a below market contract liability.

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No definition available.

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Costs related to the impairment of oil and gas properties, net of taxes.

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No definition available.

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Represents the amount of costs related to severance and other obligations incurred during the reporting period.

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Restructuring and Asset Impairments (Details) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended		0 Months Ended	3 Months Ended
Restructuring and Asset Impairments (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2012	Aug. 25, 2014	Jun. 30, 2014
Asset impairment and restructuring
Proceeds from sale of property, plant and equipment		$ 30,112,000	$ 0	$ 0
Property, plant and equipment, net		1,466,297,000us-gaap_PropertyPlantAndEquipmentNet	1,637,552,000us-gaap_PropertyPlantAndEquipmentNet		1,466,297,000us-gaap_PropertyPlantAndEquipmentNet
Asset impairment charges		51,556,000us-gaap_AssetImpairmentCharges	0us-gaap_AssetImpairmentCharges	43,103,000us-gaap_AssetImpairmentCharges
Restructuring and impairment charge		57,508,000	2,883,000	1,113,479,000
Write-off capitalized exploratory costs associated with natural gas exploration project, net of taxes	40,000,000
Write-off capitalized exploratory costs associated with natural gas exploration project, net of taxes	25,000,000
Canadian and U.K. Operations
Asset impairment and restructuring
Restructuring and impairment charge		4,721,000	10,646,000	999,198,000
Willow Creek Mine \| Corporate, Non-Segment
Asset impairment and restructuring
Curtailment costs		500,000
Willow Creek Mine \| Closure
Asset impairment and restructuring
Curtailment costs			10,700,000
Willow Creek Mine \| Canadian and U.K. Operations
Asset impairment and restructuring
Curtailment costs		4,700,000
Willow Creek Mine \| U.S.
Asset impairment and restructuring
Curtailment costs		700,000
North River Mine \| Closure
Asset impairment and restructuring
Gain on release of a below market contract liability			17,000,000
Asset impairment charges			9,300,000		28,500,000
Aberpergwm underground coal mine \| Closure
Asset impairment and restructuring
Asset impairment charges						3,100,000
Restructuring and impairment charge						9,100,000
Severance and other obligations						6,000,000
BCCT
Asset impairment and restructuring
Proceeds from sale of property, plant and equipment							25,000,000
Impairment charge recognized								23,100,000
Property, plant and equipment, net			$ 47,500,000