Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 45	$ 7,701
Gross unrealized gain	0	41
Gross unrealized loss	0	0
Fair value, investments	45	7,742
Less cash equivalents, Carrying amount	8,785	1,057	$ 963
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	797	667
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	797	667
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,734	7,656
Gross unrealized gain	0	41
Gross unrealized loss	0	0
Fair value, investments	7,734	7,697
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	45	45
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	45	45
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	8,576	8,368
Gross unrealized gain	0	41
Gross unrealized loss	0	0
Fair value, investments	8,576	8,409
Less Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Less cash equivalents, Carrying amount	8,531	667
Less cash equivalents, Fair value	$ 8,531	$ 667