Income Taxes (Schedule Of Components Of Income Tax Expense By Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Abstract]
Statutory income tax expense	$ 27,844	$ 26,991	$ 29,469
State income tax expense, net of federal income tax expense	5,483	4,847	3,596
Domestic production activities deduction			(2,513)
Executive compensation	4,123	2,760
Excess tax benefits upon vesting of share based payment awards	(252)	(1,276)
Remeasurement of deferred tax assets		1,548	2,790
Federal energy credits	(17,256)	(2,426)
Other permanent items	(301)	(369)	527
Income tax expense	$ 19,641	$ 32,075	$ 33,869