Income Taxes (Schedule Of Components Of Income Tax Expense By Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Abstract]
Statutory income tax expense	$ 25,602	$ 21,107	$ 10,836
State income tax expense, net of federal income tax expense	1,954	1,690	643
Domestic production activities deduction	(2,146)	(1,766)	(612)
Federal energy credits	(1,944)
Other permanent items	221	37	70
Other adjustments	(78)	(653)
Income tax expense	$ 23,609	$ 20,415	$ 10,937