Investment Securities (Summary Of Maturity Dates Of Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than one year	$ 14,176	$ 23,451
1-5 years		8,629
Total	14,176	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	2,496	8,461
Total	2,496	8,461
Corporate Notes And Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than one year	11,680	14,990
1-5 years		8,629
Total	$ 11,680	$ 23,619