Note 7 - Revenue 1 (Details Textual) - Coal [Member] - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Jan. 01, 2021
Accounts Receivable, after Allowance for Credit Loss, Total					$ 14.4
Revenue from Contract with Customer Benchmark [Member] \| Geographic Concentration Risk [Member] \| INDIANA
Concentration Risk, Percentage	70.00%	67.00%	79.00%	72.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
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