Note 8 - Asset Retirement Obligations (Details Textual) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Gain (Loss) on Disposition of Degasification Wells	$ (18,311)	$ 0

The amount of gain (loss) on disposition of degasification wells.

No definition available.

Name:	ceix_GainLossOnDispositionOfDegasificationWells
Namespace Prefix:	ceix_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration