Other Short-Term and Long-Term Obligations (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Other Short-Term and Long-Term Obligations
Federal coal lease obligations, current	$ 63,191	$ 63,191
Federal coal lease obligations, noncurrent	122,928	122,928
Total principal payments	$ 186,119	$ 186,119

Current and non-current portion of amounts payable related to the acquisition of mineral extraction rights from the Federal government. This includes principal and imputed interest.

No definition available.

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