Accounting For Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal income taxes at statutory rates	$ 75,391	$ 64,967	$ 67,237
Federal income taxes at statutory rates	35.00%	35.00%	35.00%
Tax effect of regulatory treatment of utility plant differences	$ 3,297	$ 4,358	$ 4,008
Tax effect of regulatory treatment of utility plant differences	1.50%	2.30%	2.10%
State income tax expense	$ 1,316	$ 1,012	$ 506
State income tax expense	0.60%	0.50%	0.20%
Settlement of prior year tax returns and adjustment of tax reserves	$ 13	$ (992)	$ 1,104
Settlement of prior year tax returns and adjustment of tax reserves	0.00%	(0.50%)	0.60%
Manufacturing deduction	$ 0	$ (1,198)	$ (169)
Manufacturing deduction	(0.00%)	(0.60%)	(0.10%)
Income Tax Reconciliation Settlement of Share Based Compensation Amount	$ (1,597)	$ 0	$ 0
Income Tax Reconciliation Settlement of Share Based Compensation Percent	(0.70%)	(0.00%)	(0.00%)
Other	$ (334)	$ (698)	$ (446)
Other	(0.10%)	(0.40%)	(0.20%)
Total income tax expense	$ 78,086	$ 67,449	$ 72,240
Effective Income Tax Rate Reconciliation, Percent	36.30%	36.30%	37.60%