Cash Equivalents And Restricted Securities (Summary Of Cash Equivalents And Restricted Securities) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash Equivalents, Cost Basis	$ 64,635	$ 34,294	$ 37,177	$ 42,236
Cost Basis	11,996	2,000
Restricted Securities, Cost Basis	513	528
Unrealized Holding Gains (Losses)
Estimated Market Value	11,996	2,000
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash Equivalents, Cost Basis	11,483	1,472
Restricted Securities, Cost Basis	513	528
Unrealized Holding Gains (Losses)
Cash Equivalents, Estimated Market Value	11,483	1,472
Restricted Securities, Estimated Market Value	$ 513	$ 528