Segment Information (Details)	9 Months Ended
Sep. 30, 2013 segments
Segment Reporting [Abstract]
Number of reportable segments	2
Western Coal Operations
Segment Information
Number of surface mines	2
Eastern Coal Operations
Segment Information
Number of surface mines	24
Number of underground mines	60

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration