Note 14 - Derivatives (Details Textual) T in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2022 USD ($) T	Mar. 31, 2021 USD ($)
Derivative, Gain (Loss) on Derivative, Net, Total	$ (188,154)	$ 0
Unrealized Gain (Loss) on Derivatives and Commodity Contracts, Total	(101,902)	$ (0)
Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net, Total	(86,252)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts, Total	$ (101,902)
Coal Contract [Member] \| Short [Member]
Derivative, Nonmonetary Notional Amount, Mass (US Ton) \| T	1,300
Coal Contract [Member] \| Long [Member]
Derivative, Nonmonetary Notional Amount, Mass (US Ton) \| T	450

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959

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- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

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- Definition

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.

+ References

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

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