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Represents the coal supply commitment as of the specified date.

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Represents amortization expense for contract with customer.

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Represents the number of major customers accounting for 10% or more of the specified concentration risk benchmark, which includes, but not limited to, sales revenue, accounts receivable, etc.

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No definition available.

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Represents the quantity of priced coal supply commitment.

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No definition available.

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Represents the amount of asset retirement obligations before discounting.

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Represents the year in which supply commitments end.

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Amount of allowance for credit loss on accounts receivable.

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- Definition

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.

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Value of input used to measure debt instrument, including, but not limited to, convertible and non-convertible debt.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands, T in Millions	12 Months Ended		24 Months Ended		31 Months Ended
	Dec. 31, 2023 USD ($) T	Dec. 31, 2022 USD ($)	Dec. 31, 2028	Dec. 31, 2026	Dec. 31, 2025	May 31, 2023 USD ($)
Number of Reportable Segments	2
Accounts Receivable, Allowance for Credit Loss, Ending Balance	$ 0	$ 0
Regulatory Asset	37,500
Undiscounted Asset Retirement Obligations	$ 26,600	$ 27,000
Capacity Payment Reductions						$ 7,500
Coal Supply Commitment (US Ton) \| T	9.2
Priced Coal Supply Commitment (US Ton) \| T	6.2
Year Supply Commitments End	2028
Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Coal [Member]
Number of Major Customers	5	5
Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Coal [Member] \| Five Customers [Member]
Concentration Risk, Percentage	93.00%	90.00%
Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Electric Distribution [Member]
Number of Major Customers	2	1
Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Electric Distribution [Member] \| One Customer [Member]
Concentration Risk, Percentage	100.00%	100.00%
Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Electric Distribution [Member] \| Three Customers [Member]
Concentration Risk, Percentage	91.00%
Number of Major Customers	3
Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Energy Output [Member] \| Forecast [Member]
Concentration Risk, Percentage					22.00%
Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Energy Capacity [Member] \| Forecast [Member]
Concentration Risk, Percentage			28.00%		32.00%
Revenue, Product and Service Benchmark [Member] \| Product Concentration Risk [Member] \| Electricity, Generation [Member]
Concentration Risk, Percentage	100.00%
Accounts Receivable [Member] \| Customer Concentration Risk [Member] \| Coal [Member]
Number of Major Customers	4	4
Accounts Receivable [Member] \| Customer Concentration Risk [Member] \| Coal [Member] \| Five Customers [Member]
Concentration Risk, Percentage	85.00%	86.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	2 years
Minimum [Member] \| Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Energy Capacity [Member] \| Forecast [Member]
Concentration Risk, Percentage				47.00%
Minimum [Member] \| Measurement Input, Discount Rate [Member]
ARO measurement input	7
Minimum [Member] \| Surface and Underground Mining Equipment [Member]
Property, Plant and Equipment, Useful Life (Year)	3 years
Minimum [Member] \| Power Plant Equipment [Member]
Property, Plant and Equipment, Useful Life (Year)	4 years
Maximum [Member]
Coal Supply Commitment (US Ton) \| T	10.7
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	4 years
Maximum [Member] \| Revenue, Product and Service Benchmark [Member] \| Customer Concentration Risk [Member] \| Energy Capacity [Member] \| Forecast [Member]
Concentration Risk, Percentage				55.00%
Maximum [Member] \| Measurement Input, Discount Rate [Member]
ARO measurement input		0.10
Maximum [Member] \| Surface and Underground Mining Equipment [Member]
Property, Plant and Equipment, Useful Life (Year)	25 years
Maximum [Member] \| Power Plant Equipment [Member]
Property, Plant and Equipment, Useful Life (Year)	9 years
Coal Purchase Agreement [Member]
Contract with Customer, Asset, Amortized Expense	$ 19,600	$ 14,700
Coal Purchase Agreement [Member] \| Operating Expense [Member]
Contract with Customer, Asset, Amortized Expense	30,700	3,600
Power Purchase Agreement [Member]
Contract with Customer, Liability, Amortization Expense	$ 70,500	$ 23,300
Sunrise Energy, LLC [Member]
Equity Method Investment, Ownership Percentage	50.00%