Note 7 - Revenue 1 (Details Textual) - Coal [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2020
Accounts Receivable, after Allowance for Credit Loss, Total			$ 14.4
INDIANA \| Revenue from Contract with Customer Benchmark [Member] \| Geographic Concentration Risk [Member]
Concentration Risk, Percentage	73.00%	74.00%

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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