Rates and Other Regulatory Activities - Additional Information (Detail)				1 Months Ended	3 Months Ended
	Feb. 19, 2016 USD ($)	Dec. 21, 2015 USD ($)	Oct. 13, 2015 dekatherm / d	Dec. 31, 2015 USD ($)	Mar. 31, 2016 dekatherm / d in mi
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%
DELAWARE
Rates and Other Regulatory Activities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount | $		$ 4,700,000
Public Utilities, Requested Rate Increase (Decrease), Percentage		10.00%
MARYLAND
Rates and Other Regulatory Activities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount | $				$ 950,000
Public Utilities, Requested Rate Increase (Decrease), Percentage				5.00%
Eastern Shore [Member]
Rates and Other Regulatory Activities [Line Items]
Volume The Expansion Project Is Expected to Provide | dekatherm / d			53,000
Total Capacity After Pipeline Improvements | dekatherm / d			160,000
White Oak Lateral Mainline Expansion [Member] | Eastern Shore [Member]
Rates and Other Regulatory Activities [Line Items]
Volume The Expansion Project Is Expected to Provide | dekatherm / d					45,000
Number of pipeline miles | mi					7.2
Lateral diamater of pipeline to be installed | in					16
Horsepower Of Additional Compression					3,550
System Reliability Project [Member] | Eastern Shore [Member]
Rates and Other Regulatory Activities [Line Items]
Number of pipeline miles | mi					10.1
Lateral diamater of pipeline to be installed | in					16