Accounting For Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income taxes at statutory rates	$ 33,467	$ 28,673	$ 47,909
Tax effect of regulatory treatment of utility plant differences	(13,820)	(12,893)	(9,967)
State income tax expense	1,385	814	1,465
Acquisition costs			(1,712)
Flow through related to deduction of meters and mixed service costs	(8,678)
Non-plant excess deferred turnaround		(8,476)	(5,690)
Tax loss on sale of METALfx			(1,272)
Customer refunds related to prior years at 35 percent		(1,189)
Other	(323)	122	641
Total income tax expense	$ 12,031	$ 7,051	$ 31,374
Federal statutory tax rate	21.00%	21.00%	21.00%	21.00%	35.00%
Tax effect of regulatory treatment of utility plant differences	(8.70%)	(9.40%)	(4.30%)
State income tax expense	0.80%	0.60%	0.60%
Acquisition costs			(0.70%)
Flow through related to deduction of meters and mixed service costs	(5.40%)
Non-plant excess deferred turnaround		(6.20%)	(2.50%)
Tax loss on sale of METALfx			(0.60%)
Customer refunds related to prior years at 35 percent		(0.90%)
Other	(0.20%)	0.10%	0.30%
Effective Income Tax Rate Reconciliation, Percent	7.50%	5.20%	13.80%