Cash Equivalents And Restricted Securities (Summary Of Cash Equivalents And Restricted Securities) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash Equivalents, Cost Basis	$ 25,719	$ 40,753	$ 52,507	$ 56,642
Restricted Securities, Cost Basis	759	776
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash Equivalents, Cost Basis	375	372
Restricted Securities, Cost Basis	759	776
Unrealized Holding Gains
Cash Equivalents, Estimated Market Value	375	372
Restricted Securities, Estimated Market Value	$ 759	$ 776