Income Taxes (Schedule Of Components Of Income Tax Expense By Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Statutory income tax expense	$ 26,991	$ 29,469	$ 25,602
State income tax expense, net of federal income tax expense	4,847	3,596	1,954
Domestic production activities deduction		(2,513)	(2,146)
Executive compensation	2,760
Excess tax benefits upon vesting of share-based payment awards	(1,276)
Remeasurement of deferred tax assets	1,548	2,790
Federal energy credits	(2,426)		(1,944)
Other permanent items		248	221
Other adjustments		279
Other adjustments	(369)		(78)
Income tax expense	$ 32,075	$ 33,869	$ 23,609