Other Commitments and Contingencies - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Other Commitments [Line Items]
Debt Service Coverage Ratio	1.25
Debt Service Coverage Ratio Measurement Period	12
Maximum Days To Make Default Good	5 days
Ratio based on average number of prior quarters	6
Ratios based on average of the prior quarters	1 year 6 months
Funds from operations interest coverage ratio minimum times	2
Total debt to capital maximum	0.65
Number Of Years For Power Purchase Agreement	20 years
Contract Duration	20 years
Aggregate guaranteed amount	$ 37.0
Draws on letters of credit	5.4
Guarantor Obligations, Current Carrying Value	17.9
Guarantor Obligations, Current Carrying Value, PESCO	$ 6.8
Florida Natural Gas Distribution and Eight Flags [Member]
Other Commitments [Line Items]
Number of Years for Asset Management Agreement	10 years
Delmarva [Member]
Other Commitments [Line Items]
Number of Years for Asset Management Agreement	3 years