Financial Instruments And Investments (Contractual Year For Maturity Of Available-For-Sale Securities ) (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Total	$ 136,982
2019	3,945
2020 through 2023	45,924
2024 through 2028	36,850
2029 and Beyond	50,263
Federal Agency Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Total	30,363
2019	0
2020 through 2023	19
2024 through 2028	514
2029 and Beyond	29,830
U.S. Government Bonds
Debt Securities, Available-for-sale [Line Items]
Total	49,402
2019	2,356
2020 through 2023	20,491
2024 through 2028	21,282
2029 and Beyond	5,273
Municipal Obligations
Debt Securities, Available-for-sale [Line Items]
Total	9,548
2019	649
2020 through 2023	3,446
2024 through 2028	3,566
2029 and Beyond	1,887
Corporate Obligations
Debt Securities, Available-for-sale [Line Items]
Total	47,669
2019	940
2020 through 2023	21,968
2024 through 2028	11,488
2029 and Beyond	$ 13,273

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