Derivatives (Narrative) (Details) gal in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) gal
2021
Derivative [Line Items]
Value of trading portfolio realized - gains (losses) | $	$ 0.3
Diesel Purchases | Heating Oil
Derivative [Line Items]
Quantities under derivative contracts (in gallons)	0
Diesel Purchases | Minimum
Derivative [Line Items]
Diesel fuel purchased annually (in gallons)	30
Diesel Purchases | Maximum
Derivative [Line Items]
Diesel fuel purchased annually (in gallons)	35