Investment Securities (Summary Of Maturity Dates Of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than one year	$ 23,451	$ 38,093
1-5 years	8,629
Total	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	8,461
Total	8,461
Corporate Notes And Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than one year	14,990
1-5 years	8,629
Total	$ 23,619