Financial Instruments And Investments (Contractual Year For Maturity Of Available-For-Sale Securities ) (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Federal Agency Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Total	$ 25,840
2018	0
2019 through 2022	16
2023 through 2027	261
2028 and Beyond	25,563
U.S. Government Bonds
Schedule of Available-for-sale Securities [Line Items]
Total	54,548
2018	1,894
2019 through 2022	28,263
2023 through 2027	11,415
2028 and Beyond	12,976
Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Total	12,331
2018	76
2019 through 2022	5,483
2023 through 2027	5,735
2028 and Beyond	1,037
Corporate Obligations
Schedule of Available-for-sale Securities [Line Items]
Total	36,068
2018	213
2019 through 2022	17,518
2023 through 2027	7,151
2028 and Beyond	$ 11,186