Investment Securities And Short-Term Investments (Schedule Of Contractual Maturities Of Short-Term Investment Bonds) (Details)	3 Months Ended
	Mar. 31, 2020
US Treasury Securities [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Contractual maturities of bonds	1 month
US Treasury Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Contractual maturities of bonds	1 year
Corporate Bonds [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Contractual maturities of bonds	1 month
Corporate Bonds [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Contractual maturities of bonds	3 years
Government Agency Bonds [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Contractual maturities of bonds	9 months
Government Agency Bonds [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Contractual maturities of bonds	1 year