Rates and Other Regulatory Activities - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($) mi	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) dekatherm / d mi	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Rates and Other Regulatory Activities [Line Items]
Restricted Payment	$ 256,400								$ 256,400
Regulatory Assets	124,592				$ 78,551				124,592	$ 78,551
Revenues	$ 137,038	$ 101,419	$ 97,051	$ 152,690	$ 131,974	$ 92,626	$ 94,542	$ 160,464	488,198	$ 479,605	$ 490,316
Regulatory Asset - Storm Cost Recovery									45,800
Surcharge - Storm Cost Recovery									7,700
Incremental Revenue - Storm Cost Recovery									$ 3,300
Electric Limited Proceedings [Member]
Rates and Other Regulatory Activities [Line Items]
Extent of Customers Losing Service									100.00%
Amounts Spent to Restore Service									$ 65,000
Peninsula Pipeline [Member] | Callahan Project [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Pipeline Miles | mi	26								26
Diameter of Pipe | mi	16								16
Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
Cost Recovery, Capital									$ 500
Eastern Shore Gas Company | Del-Mar Pathway Project [Domain]
Rates and Other Regulatory Activities [Line Items]
firm natural gas transportation deliverability | dekatherm / d									14,300
Eastern Shore Gas Company | Del-Mar Pathway Project [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Pipeline Miles | mi	6								6
number of customers									4
Number of Mainline Pipeline Miles | mi	13								13
Hurricane Dorrian [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liability, Amortization Period									30 years
Regulatory Liability, Amortization Period, Revised									10 years
Asset Recovery Damaged Property Costs, Noncurrent	$ 1,200								$ 1,200
Hurricane Michael
Rates and Other Regulatory Activities [Line Items]
Regulatory Liability, Amortization Period, Low Range									6 years
Regulatory Liability, Amortization Period, Revised									10 years
TCJA
Rates and Other Regulatory Activities [Line Items]
Regulatory Liability, Amortization Period, Low Range									5 years
Regulatory Liability, Amortization Period, Revised									80 years
Florida Public Utilities Company [Member]
Rates and Other Regulatory Activities [Line Items]
Business Acquisition Premium Paid	34,200								$ 34,200
Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
One time bill credit related to TCJA	900								900
Maryland Division [Member]
Rates and Other Regulatory Activities [Line Items]
One time bill credit related to TCJA	365								365
Sandpiper [Member]
Rates and Other Regulatory Activities [Line Items]
One time bill credit related to TCJA	608								608
Delaware natural gas division [Member]
Rates and Other Regulatory Activities [Line Items]
One time bill credit related to TCJA	1,500								1,500
Elkton Gas [Member]
Rates and Other Regulatory Activities [Line Items]
One time bill credit related to TCJA	$ 47								47
Elkton Gas [Member]
Rates and Other Regulatory Activities [Line Items]
Revenues									$ 2,399
Elkton Gas [Member] | Regulated Energy [Member]
Rates and Other Regulatory Activities [Line Items]
Number of customers acquired through acquisition									7,000