Rates and Other Regulatory Activities - Additional Information (Detail) (USD $)	12 Months Ended	9 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Investment In Affiliates [Line Items]
Regulatory Assets	$ 87,103,000		$ 69,020,000
MARYLAND
Investment In Affiliates [Line Items]
Reduction in accumulated depreciation	3,000,000
PeriodWithinWhichToPerformDepreciationStudy	5 years
Florida
Investment In Affiliates [Line Items]
Reduction In Annual Depreciation Expense	1,000,000
Public Utilities Interim Rate Increase Decrease Request Amount		2,400,000
Public Utilities, Requested Rate Increase (Decrease), Amount		5,900,000
Public Utilities, Interim Rate Increase (Decrease), Amount		2,200,000
Public Utilities, Approved Rate Increase (Decrease), Amount		3,800,000
Public Utilities, Approved Return on Equity, Percentage		10.25%
Total Number Of Electricity Units Proposed To Be Purchased Under Contract	20
Term of the Power Purchase Agreement	20 years
Estimated Environmental Cleanup Costs To Be Recovered		381,000
Eastern Shore Gas Company
Investment In Affiliates [Line Items]
NumberOfDaysDuringPeakPeriodSubjectToRightNotToScheduleService		90 days
Proposed Fuel Retention Percentage Rate	0.62%
Deferred Gas Required For Operations Underrecovery Regulatory Balance	494,000
Deferred Cash Out Costs Overrecovery Regulatory Balance	160,000
Eastern Shore Gas Company | White Oak Lateral Mainline Expansion [Member]
Investment In Affiliates [Line Items]
Number of Pipeline Miles	7.2
Estimated capital costs of project	29,800,000
Lateral Diameter Of Pipeline To Be Installed	16
Horsepower of additional compression	3,550
Volume The Expansion Project Is Expected to Provide	45,000
Eastern Shore Gas Company | TETLP Expansion Project [Member]
Investment In Affiliates [Line Items]
Total Capacity After Pipeline Improvements	57,000
Additional firm transportation service capacity	107,000
Eastern Shore Gas Company | White Oak Lateral Project Filing [Member]
Investment In Affiliates [Line Items]
Additional firm transportation service capacity	55,200
Estimated capital costs of project	11,500,000
Amount Received From A State Grant	$ 2,500,000
Lateral Length Of Pipeline To Be Installed	5.5
Lateral Diameter Of Pipeline To Be Installed	16