Note 7 - Revenue 2 (Details Textual) $ in Thousands	Mar. 31, 2024 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-04-01 | Energy Obligations [Member]
Revenue, Remaining Performance Obligation, Amount	$ 111,970
Revenue, Remaining Performance Obligation, Percentage	47.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-04-01 | Contract Capacity [Member]
Revenue, Remaining Performance Obligation, Amount	$ 163,510
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	2029 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-04-01 | Fixed-Price Contract [Member]
Revenue, Remaining Performance Obligation, Amount	$ 270,200
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	3 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-04-01 | Coal Sales [Member]
Revenue, Remaining Performance Obligation, Amount	$ 155,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	2027 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01 | Contract Capacity [Member]
Revenue, Remaining Performance Obligation, Amount	$ 186,600
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	1 year
Hoosier [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-04-01 | Energy Obligations [Member]
Revenue, Remaining Performance Obligation, Amount	$ 99,300
Hoosier [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-04-01 | Contract Capacity [Member]
Revenue, Remaining Performance Obligation, Amount	$ 35,200
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year)	1 year
Hoosier [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01 | Contract Capacity [Member]
Revenue, Remaining Performance Obligation, Amount	$ 60,900