Note 13 - Derivatives (Details Textual) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Derivative, Gain (Loss) on Derivative, Net, Total	$ (68,352)	$ (20,437)	$ (256,506)	$ (20,437)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts, Total	5,571	(20,437)	(96,331)	(20,437)
Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net, Total	(73,923)		(160,175)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts, Total	$ (5,571)	$ (20,437)	$ (96,331)	$ (20,437)

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open derivatives, commodity, or energy contracts, held at each balance sheet date, that was included in earnings for the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

Name:	us-gaap_UnrealizedGainLossOnDerivativesAndCommodityContracts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration