Accounting For Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended			24 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal income taxes at statutory rates	$ 47,909	$ 34,158	$ 69,542
Federal income taxes at statutory rates	21.00%	21.00%	35.00%	21.00%
Tax effect of regulatory treatment of utility plant differences	$ (9,967)	$ (8,153)	$ 3,482
Tax effect of regulatory treatment of utility plant differences	(4.30%)	(5.00%)	1.70%
State income tax expense	$ 1,465	$ 1,191	$ 1,110
State income tax expense	0.60%	0.70%	0.60%
Settlement of prior year tax returns and adjustment of tax reserves	$ 643	$ (140)	$ (384)
Settlement of prior year tax returns and adjustment of tax reserves	0.30%	(0.10%)	(0.20%)
Manufacturing deduction	$ 0	$ 0	$ (1,119)
Manufacturing deduction	0.00%	0.00%	(0.60%)
Settlement of equity awards	$ 612	$ (990)	$ (1,439)
Settlement of equity awards	0.30%	(0.60%)	(0.70%)
Acquisition costs	$ (1,712)	$ 329	$ 2,491
Acquisition costs	(0.70%)	0.20%	1.30%
Federal income tax rate change	$ 0	$ 0	$ 10,169
Federal income tax rate change	0.00%	0.00%	5.10%
Non-plant excess deferred turnaround	$ (5,690)	$ 0	$ 0
Non-plant excess deferred turnaround	(2.50%)	0.00%	0.00%
Tax loss on sale of METALfx	$ (1,272)	$ 0	$ 0
Tax loss on sale of METALfx	(0.60%)	0.00%	0.00%
Valuation allowance	$ 267	$ 0	$ 0
Valuation allowance	0.10%	0.00%	0.00%
Other	$ (881)	$ (335)	$ (1,094)
Other	(0.40%)	(0.20%)	(0.50%)
Total income tax expense	$ 31,374	$ 26,060	$ 82,758
Effective Income Tax Rate Reconciliation, Percent	13.80%	16.00%	41.70%