Financial Instruments And Investments (Contractual Year For Maturity Of Available-For-Sale Securities ) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	$ 16,584
2018	511
2019 through 2022	7,690
2023 through 2027	7,064
2028 and Beyond	1,319
Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Total	34,674
2018	215
2019 through 2022	16,946
2023 through 2027	7,601
2028 and Beyond	9,912
U.S. Government Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	58,181
2018	5,251
2019 through 2022	27,181
2023 through 2027	11,663
2028 and Beyond	14,086
Collateralized Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Total	20,732
2018	0
2019 through 2022	18
2023 through 2027	280
2028 and Beyond	$ 20,434