Accounting For Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal income taxes at statutory rates	$ 64,967	$ 67,237	$ 56,821
Federal income taxes at statutory rates	35.00%	35.00%	35.00%
Tax effect of regulatory treatment of utility plant differences	$ 4,358	$ 4,008	$ 3,532
Tax effect of regulatory treatment of utility plant differences	2.30%	2.10%	2.20%
State income tax expense	$ 1,012	$ 506	$ 1,553
State income tax expense	0.50%	0.20%	1.00%
Settlement of prior year tax returns and adjustment of tax reserves	$ (992)	$ 1,104	$ (1,104)
Settlement of prior year tax returns and adjustment of tax reserves	(0.50%)	0.60%	(0.70%)
Manufacturing deduction	$ (1,198)	$ (169)	$ (2,033)
Manufacturing deduction	(0.60%)	(0.10%)	(1.30%)
Other	$ (698)	$ (446)	$ (755)
Other	(0.40%)	(0.20%)	(0.50%)
Total income tax expense	$ 67,449	$ 72,240	$ 58,014
Effective Income Tax Rate Reconciliation, Percent	36.30%	37.60%	35.70%