Federal Coal Lease Obligations (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Federal Coal Lease Obligations
Federal coal lease obligations, current	$ 0	$ 63,970

Current portion of amounts payable related to the acquisition of mineral extraction rights from the Federal government. This includes principal only.

No definition available.

Name:	cld_FederalCoalLeaseObligationsCurrent
Namespace Prefix:	cld_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant