Rates and Other Regulatory Activities - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) mi	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) dekatherm / d unit mi	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Rates and Other Regulatory Activities [Line Items]
Restricted Payment	$ 201,500,000								$ 201,500,000
Regulatory Assets	77,218,000				$ 86,505,000				$ 77,218,000	$ 86,505,000
Florida Appeal Period for Federal Tax Reform Impact									30 days
Revenues	$ 201,190,000	$ 140,279,000	$ 136,664,000	$ 239,356,000	$ 180,403,000	$ 126,936,000	$ 125,084,000	$ 185,160,000	$ 717,489,000	$ 617,583,000	$ 498,860,000
Electric Limited Proceedings [Member]
Rates and Other Regulatory Activities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 1.82
Number of Years to Recover Storm Related Costs									2 years
Extent of Customers Losing Service									100.00%
Amounts Spent to Restore Service									$ 60,000,000
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									$ 30,000,000
Asset Recovery Damaged Property Costs, Noncurrent	$ 1,500,000								1,500,000
Deferred Storm and Property Reserve Deficiency, Noncurrent	779,000								779,000
Electric distribution
Rates and Other Regulatory Activities [Line Items]
Amount of Regulatory Costs Not yet Approved	15,200,000								15,200,000
Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
Increase in Revenue Recognized Due to Motion Rate in Effect	$ 3,700,000								$ 3,700,000
Eastern Shore Gas Company | 2017 Expansion Project [Member]
Rates and Other Regulatory Activities [Line Items]
firm natural gas transportation deliverability | dekatherm / d									61,162
Additional Firm Natural Gas Transportation Deliverability | dekatherm / d									52,500
Number of Pipeline Miles | mi	23								23
Miles Of Natural Gas Pipeline | mi	17								17
Pressure Control Stations									2
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	$ 2,500,000								$ 2,500,000
Business Acquisition Premium Paid	$ 34,200,000								$ 34,200,000
Subscribers [Member] | Eastern Shore Gas Company | 2017 Expansion Project [Member]
Rates and Other Regulatory Activities [Line Items]
number of customers									7
Number of affiliates | unit									3
Pre TCJA approved revenue requirements [Member] | Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount									$ 9,800,000
Post TCJA approved revenue requirements [Member] | Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount									$ 6,600,000