Investments (Cost And Estimated Fair Value Of Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 7,450	$ 7,473
Gross unrealized gain	24	8
Gross unrealized loss	(54)	(54)
Fair value, investments	7,420	7,427
Cash equivalents, Carrying amount	1,185	840	$ 792	$ 569
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	693	348
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value, investments	693	348
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	7,396	7,419
Gross unrealized gain	24	8
Gross unrealized loss	0	0
Fair value, investments	7,420	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	8,143	7,821
Gross unrealized gain	24	8
Gross unrealized loss	(54)	(54)
Fair value, investments	8,113	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	693	348
Cash equivalents, Fair value	$ 693	$ 348