Investment Securities (Summary Of Maturity Dates Of Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 15,177	$ 8,523
Less than one year	16,889	23,451
1-5 years	5,379	8,629
Total	22,268	32,080
Commercial Paper Original Maturities of 91 Days or More [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than one year	1,897	8,461
Total	1,897	8,461
Corporate Notes And Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than one year	14,992	14,990
1-5 years	5,379	8,629
Total	$ 20,371	$ 23,619