Cash Equivalents And Restricted Securities (Summary Of Cash Equivalents And Restricted Securities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash Equivalents, Cost Basis	$ 39,977	$ 56,642	$ 37,588	$ 33,375
Restricted Securities, Cost Basis	776	699
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cost Basis		699
Unrealized Holding Gains
Restricted Securities, Estimated Market Value		699
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash Equivalents, Cost Basis	372	3,466
Restricted Securities, Cost Basis	776
Unrealized Holding Gains
Cash Equivalents, Estimated Market Value	372	$ 3,466
Restricted Securities, Estimated Market Value	$ 776