Goodwill, net Goodwill, net (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Goodwill [Line Items]
Goodwill impairment	$ 253,102	$ 0	$ 253,102	$ 1,525,332	$ 1,713,526
Eastern Coal Operations [Member]
Goodwill [Line Items]
Goodwill impairment	$ 253,102		$ 253,102	$ 1,525,332	$ 1,660,218

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Section 45

-Paragraph 28

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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