Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 7,458	$ 7,473
Gross unrealized gain	14	8
Gross unrealized loss	(54)	(54)
Fair value, investments	7,418	7,427
Cash equivalents, Carrying amount	895	840	$ 560	$ 569
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	376	348
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	376	348
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,404	7,419
Gross unrealized gain	14	8
Gross unrealized loss	0	0
Fair value, investments	7,418	7,427
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	54	54
Gross unrealized gain	0	0
Gross unrealized loss	(54)	(54)
Fair value, investments	0	0
Debt and Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,834	7,821
Gross unrealized gain	14	8
Gross unrealized loss	(54)	(54)
Fair value, investments	7,794	7,775
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	376	348
Cash equivalents, Fair value	$ 376	$ 348