Short-Term Debt and Long-term Debt (Long Term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Weighted Average Rate	2.16%	2.18%
Amount	$ 245,800	$ 245,800
Maturing by December 31, 2019 [Member]
Debt Instrument [Line Items]
Weighted Average Rate		1.86%
Amount		$ 50,000
Maturing by December 31, 2020 [Member]
Debt Instrument [Line Items]
Weighted Average Rate	1.85%	1.85%
Amount	$ 50,000	$ 50,000
Maturing by December 31, 2021 [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.19%	2.19%
Amount	$ 68,000	$ 68,000
Maturing by December 31, 2022 [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.32%	2.45%
Amount	$ 67,800	$ 52,800
Maturing by December 31, 2023 [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.56%	2.90%
Amount	$ 35,000	$ 25,000
Maturing by December 31, 2024 [Member]
Debt Instrument [Line Items]
Weighted Average Rate	1.75%
Amount	$ 25,000