Note 6 - Revenue 1 (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Accounts Receivable, after Allowance for Credit Loss, Total	$ 14,300,000
Contract Capacity [Member]
Contract with Customer, Liability	$ 23,100,000
Coal [Member] | INDIANA | Revenue from Contract with Customer Benchmark [Member] | Geographic Concentration Risk [Member]
Concentration Risk, Percentage	33.00%	74.00%
Delivered Energy [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 211,800,000	$ 53,900,000
Capacity Payments [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 56,100,000	$ 12,300,000
Electricity, Purchased [Member] | Hoosier [Member]
Long-Term Purchase Commitment, Minimum Quantity Required, Percentage	70.00%
Long-term Purchase Commitment, Minimum Quantity Required, Price Per Megawatt Hour	$ 34
Long-term Purchase Commitment, Stand Ready Obligation, Contract Capacity, Megawatts Provided Year One	917
Long-term Purchase Commitment, Stand Ready Obligation, Contract Capacity, Megawatts Provided Year Two Through Four	300
Long-term Purchase Commitment, Stand Ready Obligation, Contract Capacity, Price Per Kilowatts-month	$ 5.8