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Note 6 - Revenue 1 (Details Textual) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Jan. 01, 2023	Jan. 01, 2021
Coal [Member]
Accounts Receivable, after Allowance for Credit Loss, Total				$ 12.8
Contract with Customer, Liability			$ 8.9
Contract with Customer, Liability, Revenue Recognized	$ 2.5
Coal [Member] \| Geographic Concentration Risk [Member] \| INDIANA \| Revenue from Contract with Customer Benchmark [Member]
Concentration Risk, Percentage	52.00%	87.00%
Electric Operations [Member]
Contract with Customer, Liability			$ 26.6
Contract with Customer, Liability, Revenue Recognized	$ 16.0
Electric Operations [Member] \| Geographic Concentration Risk [Member] \| INDIANA \| Revenue from Contract with Customer Benchmark [Member]
Concentration Risk, Percentage	100.00%