Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 5,053	$ 8,052
Gross unrealized gain	0	1
Gross unrealized loss	(12)	(12)
Fair value, investments	5,041	8,041
Cash equivalents, Carrying amount	4,620	1,090	$ 7,062	$ 8,785
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	1,420	718
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	1,420	718
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,999	7,998
Gross unrealized gain	0	1
Gross unrealized loss	0	0
Fair value, investments	7,999	7,999
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	54	54
Gross unrealized gain	0	0
Gross unrealized loss	(12)	(12)
Fair value, investments	42	42
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	9,473	8,770
Gross unrealized gain	0	1
Gross unrealized loss	(12)	(12)
Fair value, investments	9,461	8,759
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	4,420	718
Cash equivalents, Fair value	$ 4,420	$ 718