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Income Taxes - Effective Income Tax Rate (Details)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Federal Statutory Rate	21.00%	21.00%
Increases (Decreases) in Tax from:
State Taxes on Income, Net of Federal Tax	5.00%	5.00%
Production Tax Credits (PTCs)	(4.40%)	(7.60%)
Amortization of Excess Deferred Income Taxes	(1.30%)	(2.90%)
Excess Tax Deduction on Stock Awards	(0.50%)	(0.10%)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax	(0.20%)	(0.40%)
Corporate-Owned Life Insurance	0.20%	(0.50%)
Other, Net	(0.10%)	0.30%
Effective Tax Rate	19.70%	14.80%

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Effective Income Tax Rate Reconciliation, Corporate-Owned Life Insurance, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other tax credits.

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