Vectren Fuels Acquisition (Schedule of Business Acquisition) (Details) (Vectren Fuels [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Assets received:
Accounts receivable	$ 16,879
Advance royalties	711
Prepaid expense	701
Land and mineral rights	87,293
Mine development	37,485
Building and equipment	152,977
Total assets received	330,710
Liabilities assumed:
Accounts payable and accrued liabilities	12,707
Asset retirement obligations	6,550
Total liabilities assumed	19,257
Total consideration paid	311,453
Coal [Member]
Assets received:
Inventory	21,484
Replacement Parts [Member]
Assets received:
Inventory	$ 13,180

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Amount of Mine Debelopment acquired, at the acquisition date

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Amount of assets acquired at the acquisition date.

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Amount of other assets expected to be realized or consumed before one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of liabilities incurred for goods and services received that are used in an entity's business and related party payables, assumed at the acquisition date.

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The amount of inventory recognized as of the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Amount of other liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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