Rates and Other Regulatory Activities - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($) mi	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) dekatherm / d mi	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Rates and Other Regulatory Activities [Line Items]
Restricted Payment	$ 227,500								$ 227,500
Regulatory Assets	78,551				$ 77,218				78,551	$ 77,218
Revenues	$ 131,973	$ 92,626	$ 94,541	$ 160,464	$ 134,214	$ 93,400	$ 93,872	$ 168,831	479,604	$ 490,316	$ 449,646
Depreciation Expense Decrease from Depreciation Study Rate Change									$ 900
Electric Limited Proceedings [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Years to Recover Storm Related Costs									2 years
Extent of Customers Losing Service									100.00%
Amounts Spent to Restore Service									$ 65,000
Number of Term Notes Issued for Hurricane Michael	2								2
Number of Months for Term Notes to Finance Hurricane Michael									13 months
Dollar Amount of Term Notes to Finance Hurricane Michael Costs									$ 30,000
Asset Recovery Damaged Property Costs, Noncurrent	$ 1,500								1,500
Deferred Storm and Property Reserve Deficiency, Noncurrent	$ 800								$ 800
Basis Plus LIBOR for Term Notes to Finance Hurricane Michael Costs	75								75
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 | 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
Florida Public Utilities Company [Member]
Rates and Other Regulatory Activities [Line Items]
Restricted Payment	$ 2,500								$ 2,500
Business Acquisition Premium Paid	$ 34,200								$ 34,200
Elkton Gas [Member] | Regulated Energy [Member]
Rates and Other Regulatory Activities [Line Items]
Number of customers acquired through acquisition									7,000