Accounting For Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended			24 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income taxes at statutory rates	$ 34,158	$ 69,542	$ 75,391
Federal income taxes at statutory rates	21.00%	35.00%	35.00%	35.00%
Tax effect of regulatory treatment of utility plant differences	$ (8,153)	$ 3,482	$ 3,297
Tax effect of regulatory treatment of utility plant differences	(5.00%)	1.70%	1.50%
State income tax expense	$ 1,191	$ 1,110	$ 1,316
State income tax expense	0.70%	0.60%	0.60%
Settlement of prior year tax returns and adjustment of tax reserves	$ (140)	$ (384)	$ 13
Settlement of prior year tax returns and adjustment of tax reserves	(0.10%)	(0.20%)	0.00%
Manufacturing deduction	$ 0	$ (1,119)	$ 0
Manufacturing deduction	(0.00%)	(0.60%)	(0.00%)
Settlement of equity awards	$ (990)	$ (1,439)	$ (1,597)
Settlement of equity awards	(0.60%)	(0.70%)	(0.70%)
Acquisition costs	$ 329	$ 2,491	$ 0
Acquisition costs	0.20%	1.30%	0.00%
Federal income tax rate change	$ 0	$ 10,169
Federal income tax rate change	0.00%	5.10%
Other	$ (335)	$ (1,094)	$ (334)
Other	(0.20%)	(0.50%)	(0.10%)
Total income tax expense	$ 26,060	$ 82,758	$ 78,086
Effective Income Tax Rate Reconciliation, Percent	16.00%	41.70%	36.30%