Commitments (Details Textual) (Long-term transportation contracts [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Long-term transportation contracts [Member]
Commitments (Textual)
Liability related to firm transportation contracts assumed	$ 1.5

Represents the amount of liability related to the firm transportation contracts assumed.

No definition available.

Name:	crbo_FirmTransportationContractsLiability
Namespace Prefix:	crbo_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant