Income Taxes - Effective Income Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes at Federal Statutory Rate	21.00%	21.00%
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income Taxes at Federal Statutory Rate	$ 15,915	$ 18,823
State Taxes on Income, Net of Federal Tax	3,789	4,482
Production Tax Credits (PTCs)	(4,655)	(3,967)
Amortization of Excess Deferred Income Taxes	(798)	(1,177)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax	(164)	(200)
Allowance for Equity Funds Used During Construction	(51)	(93)
Other, Net	(732)	(238)
Income Tax Expense / Effective Tax Rate	$ 13,304	$ 17,630
Increases (Decreases) in Tax from:
State Taxes on Income, Net of Federal Tax	5.00%	5.00%
Production Tax Credits (PTCs)	(6.10%)	(4.40%)
Amortization of Excess Deferred Income Taxes	(1.10%)	(1.30%)
North Dakota Wind Tax Credit Amortization, Net of Federal Tax	(0.20%)	(0.20%)
Allowance for Equity Funds Used During Construction	(0.10%)	(0.10%)
Other, Net	(0.90%)	(0.30%)
Income Tax Expense / Effective Tax Rate	17.60%	19.70%