Income Taxes - Schedule of Income Tax Expense (Benefit) Statutory Rate vs Actual Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Computed tax at federal statutory rate
Computed tax at federal statutory rate	$ 41,719	$ 71,469	$ 25,924
Federal statutory rate	21.00%	21.00%	21.00%
Increases (reductions) resulting from:
State income taxes, net of federal income tax	$ 4,047	$ 3,605	$ 2,484
State income taxes, net of federal income tax, rate	2.00%	1.10%	2.00%
State investment tax credit, net of federal income tax	$ 2,400	$ 1,545	$ 1,624
State investment tax credit, net of federal income tax, rate	1.20%	0.50%	1.30%
Executive compensation	$ 2,111	$ 564	$ 683
Executive compensation, rate	1.10%	0.20%	0.60%
Federal renewable energy credit	$ (16,871)	$ (15,175)	$ (15,343)
Federal renewable energy credit, rate	(8.50%)	(4.50%)	(12.40%)
Excess deferred income tax amortization	$ (8,121)	$ (8,383)	$ (9,008)
Excess deferred income tax amortization, rate	(4.10%)	(2.50%)	(7.30%)
State tax rate change	$ (2,317)	$ (9)	$ (3)
State tax rate change, rate	(1.20%)	0.00%	0.00%
Research and development tax credit	$ (1,465)	$ (1,985)	$ (1,692)
Research and development tax credit, rate	(0.70%)	(0.60%)	(1.40%)
Nonqualified benefit plans	$ (1,142)	$ (1,313)	$ 1,516
Nonqualified benefit plans, rate	(0.60%)	(0.40%)	1.20%
Tax-free debt for equity exchange	$ 0	$ (38,967)	$ 0
Tax-free debt for equity exchange, rate	0.00%	(11.40%)	0.00%
Other	$ (2,772)	$ (1,138)	$ 10
Other, rate	(1.40%)	(0.30%)	0.00%
Income taxes	$ 17,589	$ 10,213	$ 6,195
Total income tax expense, rate	8.80%	3.10%	5.00%