Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 7,741	$ 7,473
Gross unrealized gain	24	8
Gross unrealized loss	(9)	(54)
Fair value, investments	7,756	7,427
Less cash equivalents, Carrying amount	963	840	$ 569
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	568	348
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	568	348
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,687	7,419
Gross unrealized gain	24	8
Gross unrealized loss	0	0
Fair value, investments	7,711	7,427
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	54	54
Gross unrealized gain	0	0
Gross unrealized loss	(9)	(54)
Fair value, investments	45	0
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	8,309	7,821
Gross unrealized gain	24	8
Gross unrealized loss	(9)	(54)
Fair value, investments	8,324	7,775
Less Cash and 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	568	348
Less cash equivalents, Fair value	$ 568	$ 348