Rates and Other Regulatory Activities - Additional Information (Detail) $ in Thousands		1 Months Ended		3 Months Ended								12 Months Ended
	Feb. 02, 2017 USD ($)	Jan. 31, 2017 USD ($)	May 31, 2013	Dec. 31, 2016 USD ($) mi	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) dekatherm / d mi in	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Rates and Other Regulatory Activities [Line Items]
Restricted Payment				$ 157,100								$ 157,100
Public Utilities, Approved Rate Increase (Decrease), Amount												2,250
Regulatory Assets				84,497				$ 85,787				84,497	$ 85,787
Revenues				$ 141,874	$ 108,348	$ 102,342	$ 146,296	$ 104,567	$ 91,913	$ 92,682	$ 170,081	498,860	$ 459,244	$ 498,834
Base Rate Filing Period			2 years 6 months
System Reliability Project [Member]
Rates and Other Regulatory Activities [Line Items]
Estimated capital costs of project												36,000
DELAWARE
Rates and Other Regulatory Activities [Line Items]
Revenues												1,500
Revenues Net Of Tax												897
Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
Estimated capital costs of project												$ 39,800
Eastern Shore Gas Company | White Oak Lateral Mainline Expansion [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Pipeline Miles | mi				7.2								7.2
Lateral Diameter Of Pipeline To Be Installed | in												16
Horsepower of additional compression												3,550
Volume The Expansion Project Is Expected to Provide | dekatherm / d												45,000
Miles Of Natural Gas Pipeline | mi				5.4								5.4
Eastern Shore Gas Company | System Reliability Project [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Pipeline Miles | mi				10.1								10.1
Lateral Diameter Of Pipeline To Be Installed | in												16
Number Of Environmental Conditions | mi				19								19
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
Estimated capital costs of project												$ 98,600
Horsepower of additional compression												3,550
Miles Of Natural Gas Pipeline | mi				17								17
number of customers												6
Subsequent Event
Rates and Other Regulatory Activities [Line Items]
Estimated capital costs of project	$ 59,800
Number Of Years In Project	5 years
Subsequent Event | Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
Cost of Services		$ 60,000
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 18,900
Public Utilities, Requested Return on Equity, Percentage		13.75%
Number Of Intervening Parties		14
Parties Filing Protest		6
Number of Months Rates Suspended		5 months
Florida Public Utilities Company [Member]
Rates and Other Regulatory Activities [Line Items]
Restricted Payment				$ 2,500								$ 2,500
Merger Related Costs Allowed To Be Recovered In Future Rates				1,300								1,300
Business Acquisition Premium Paid				$ 34,200								$ 34,200
Subscribers [Member] | Eastern Shore Gas Company | 2017 Expansion Project [Member]
Rates and Other Regulatory Activities [Line Items]
number of customers												4
landowners [Member] | Eastern Shore Gas Company | 2017 Expansion Project [Member]
Rates and Other Regulatory Activities [Line Items]
number of customers												2