Rates and Other Regulatory Activities - Additional Information (Detail)				1 Months Ended	12 Months Ended
	Feb. 19, 2016 USD ($)	Dec. 21, 2015 USD ($)	Oct. 13, 2015 dekatherm / d	Dec. 31, 2015 USD ($) mi	Dec. 31, 2015 USD ($) dekatherm / d mi in	Dec. 31, 2014 USD ($)
Rates and Other Regulatory Activities [Line Items]
Regulatory Assets				$ 85,787,000	$ 85,787,000	$ 87,103,000
DELAWARE
Rates and Other Regulatory Activities [Line Items]
Reduction In Annual Depreciation Expense		10.00%
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 4,700,000
MARYLAND
Rates and Other Regulatory Activities [Line Items]
Reduction In Annual Depreciation Expense				5.00%
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 950,000
Florida
Rates and Other Regulatory Activities [Line Items]
Reduction In Annual Depreciation Expense					$ 229,000
Eastern Shore Gas Company
Rates and Other Regulatory Activities [Line Items]
Total Capacity After Pipeline Improvements | dekatherm / d			160,000
Volume The Expansion Project Is Expected to Provide | dekatherm / d			53,000
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
Eastern Shore Gas Company | System Reliability Project [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Pipeline Miles | mi				10.1	10.1
Estimated capital costs of project					$ 32,100,000
Lateral Diameter Of Pipeline To Be Installed | in					16
Minimum [Member] | Eastern Shore Gas Company | White Oak Lateral Mainline Expansion [Member]
Rates and Other Regulatory Activities [Line Items]
Estimated capital costs of project					$ 32,000,000
Maximum [Member] | Eastern Shore Gas Company | White Oak Lateral Mainline Expansion [Member]
Rates and Other Regulatory Activities [Line Items]
Estimated capital costs of project					$ 35,000,000
Subsequent Event [Member]
Rates and Other Regulatory Activities [Line Items]
Public Utilities, Interim Rate Increase (Decrease), Amount	$ 2,500,000
Public Utilities Interim Requested Rate Increase (Decrease) Percentage	5.00%