Note 7 - Revenue 1 (Details Textual) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Jan. 01, 2023
Contract Capacity [Member]
Contract with Customer, Liability	$ 46,700,000
Delivered Energy [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	47,000,000	$ 76,400,000
Capacity Payments [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 11,800,000	$ 16,000,000
Coal [Member]
Accounts Receivable, after Allowance for Credit Loss				$ 16,300,000
Coal [Member] | INDIANA | Revenue from Contract with Customer Benchmark [Member] | Geographic Concentration Risk [Member]
Concentration Risk, Percentage	36.00%	52.00%
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