Name:	cld_NumberOfCoalDepositOptions
Namespace Prefix:	cld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of major development projects.

No definition available.

Name:	cld_NumberOfMajorDevelopmentProjects
Namespace Prefix:	cld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of surface coal mines operated by entity.

No definition available.

Name:	cld_NumberOfSurfaceCoalMinesOperatedByEntity
Namespace Prefix:	cld_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Option agreement and corresponding exploration agreement for Big Metal Development Project timing of initial term

No definition available.

Name:	cld_OptionAgreementDescriptionOfTiming
Namespace Prefix:	cld_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

Name:	cld_OrganizationAndBusinessDisclosureAbstract
Namespace Prefix:	cld_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Represents the percentage of electricity generated from the coal produced by the entity.

No definition available.

Name:	cld_PercentageOfElectricityGeneratedFromCoalProduced
Namespace Prefix:	cld_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The cash outflow from the amount invested for projects in hopes of getting a future return or interest from it.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585