Rates and Other Regulatory Activities - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) Dekatherm customer mi	Dec. 31, 2020 USD ($)
Rates and Other Regulatory Activities [Line Items]
Regulatory Asset - Storm Cost Recovery	$ 45,800
Surcharge - Storm Cost Recovery	7,700
Incremental Revenue - Storm Cost Recovery	3,300
COVID-19 Regulatory Asset	2,300	$ 1,900
Florida Public Utilities Company [Member]
Rates and Other Regulatory Activities [Line Items]
COVID-19 Settlement Amount	2,100
Delmarva [Member]
Rates and Other Regulatory Activities [Line Items]
COVID-19 Settlement Amount	300
Delaware natural gas division [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	12,626	12,728
Maryland Division [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	3,873	3,970
Sandpiper [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	3,670	3,713
Central Florida Gas Division [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	8,070	8,184
Florida Public Utilities Company [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	19,132	19,257
Fort Meade and Indiantown Divisions [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	274	309
FPU electric division [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	5,299	6,694
Eastern Shore Gas Company [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	34,190	34,190
Elkton Gas [Member]
Rates and Other Regulatory Activities [Line Items]
Regulatory Liabilities	$ 1,124	$ 1,124
Del-Mar Pathway Project [Member] | Eastern Shore Gas Company [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Mainline Pipeline Miles | mi	13
Additional Firm Natural Gas Transportation Deliverability | Dekatherm	14,300
number of customers | customer	4
Number of Pipeline Miles | mi	6
Beachside Expansion | Peninsula Pipeline Company [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Mainline Pipeline Miles | mi	11.3
Additional Firm Natural Gas Transportation Deliverability | Dekatherm	10,176
Winter Haven Expansion | Peninsula Pipeline Company [Member]
Rates and Other Regulatory Activities [Line Items]
Additional Firm Natural Gas Transportation Deliverability | Dekatherm	6,800
Regulated Energy [Member] | Escambia Meter
Rates and Other Regulatory Activities [Line Items]
Additional Firm Natural Gas Transportation Deliverability | Dekatherm	530,000