Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 1,044	$ 45
Gross unrealized gain	0	0
Gross unrealized loss	(3)	0
Fair value, investments	1,041	45
Cash equivalents, Carrying amount	7,850	8,785	$ 954	$ 1,057
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	763	797
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	763	797
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,749	7,734
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	7,749	7,734
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	45	45
Gross unrealized gain	0	0
Gross unrealized loss	(3)	0
Fair value, investments	42	45
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	8,557	8,576
Gross unrealized gain	0	0
Gross unrealized loss	(3)	0
Fair value, investments	8,554	8,576
Less Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Cash equivalents, Carrying amount	7,513	8,531
Cash equivalents, Fair value	$ 7,513	$ 8,531