Summary Of Significant Accounting Policies (Effect of the Adoption of ASC 2014-09 on Financial Statements) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes	$ 24,834	$ 24,747	$ 24,908
Deferred current revenue	8,276	9,496	9,850
Retained earnings	$ 35,920	$ 32,873	32,679
Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes			24,908
Deferred current revenue			9,850
Retained earnings			32,679
Adjustments Due To ASU 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income taxes			(161)
Deferred current revenue			(354)
Retained earnings			$ 194