Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 6,802	$ 54
Gross unrealized gain	0	0
Gross unrealized loss	(12)	(9)
Fair value, investments	6,790	45
Cash equivalents, Carrying amount	2,262	8,785	$ 1,025	$ 1,057
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	765	797
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	765	797
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,748	7,734
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	7,748	7,734
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	54	54
Gross unrealized gain	0	0
Gross unrealized loss	(12)	(9)
Fair value, investments	42	45
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	8,567	8,585
Gross unrealized gain	0	0
Gross unrealized loss	(12)	(9)
Fair value, investments	8,555	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	1,765	8,531
Cash equivalents, Fair value	$ 1,765	$ 8,531