Rate and Regulatory Matters (Schedule of Regulatory Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory Assets	$ 110,479	$ 99,236
Retirement Benefits [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 44,281	$ 39,158
Remaining recovery period	Various	Various
Income Taxes [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 60,151	$ 55,232
Remaining recovery period	Various	Various
Rate Cases, Tank Painting, and Other [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 6,047	$ 4,846
Remaining recovery period	2-10 years	2-10 years