Income Taxes - Income Tax Expense (Benefit) Statutory Rate vs Actual Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Computed tax at federal statutory rate
Computed tax at federal statutory rate	$ 113,379	$ 63,111	$ 60,074
Federal statutory rate	21.00%	21.00%	21.00%
Increases (reductions) resulting from:
State income taxes, net of federal income tax	$ 11,677	$ 9,268	$ 9,971
State income tax, rate	2.20%	3.10%	3.50%
Tax-free debt for equity exchange	$ (38,967)	$ 0	$ 0
Tax-free debt for equity exchange, rate	(0.072)	0	0
Federal renewable energy credit	$ (15,175)	$ (15,343)	$ (13,914)
Federal renewable energy credit, rate	(2.80%)	(5.10%)	(4.90%)
Excess deferred income tax amortization	$ (8,383)	$ (9,008)	$ (10,295)
Excess deferred income tax amortization, rate	(1.60%)	(3.00%)	(3.60%)
Other	$ (3,058)	$ 1,733	$ (2,292)
Other, rate	(0.60%)	0.60%	(0.80%)
Income taxes	$ 59,473	$ 49,761	$ 43,544
Total income tax expense, rate	11.00%	16.60%	15.20%