Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 7,690	$ 7,701
Gross unrealized gain	42	41
Gross unrealized loss	0	0
Fair value, investments	7,732	7,742
Cash equivalents, Carrying amount	954	1,057	$ 601	$ 963
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	722	667
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	722	667
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,645	7,656
Gross unrealized gain	42	41
Gross unrealized loss	0	0
Fair value, investments	7,687	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	8,412	8,368
Gross unrealized gain	42	41
Gross unrealized loss	0	0
Fair value, investments	8,454	8,409
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	722	667
Cash equivalents, Fair value	$ 722	$ 667