Short-term Borrowings (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Line of Credit Facility [Line Items]
Weighted average interest rate on outstanding borrowings	2.31%
Weighted average daily amounts of outstanding borrowings	$ 21.4	$ 50.0
Weighted average interest rates	2.58%	3.64%
CoBank [Member]
Line of Credit Facility [Line Items]
Renewal term of line of credit	24 months