Impact of Derivative Activity on Income and Accumulated Other Comprehensive Loss (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges	$ 0	$ 0	$ 0	$ 0
Other Derivative Instruments | Natural Gas Commodity
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities			100,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	$ 0	$ 0	$ (900,000)	$ (200,000)