Rates and Other Regulatory Activities - Additional Information (Detail) - Eastern Shore [Member] $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) dekatherm / d in mi	Dec. 31, 2014 USD ($)
White Oak Lateral Mainline Expansion [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
Estimated capital cost	$ 29.8
System Reliability Project [Member]
Rates and Other Regulatory Activities [Line Items]
Number of Pipeline Miles | mi	10.1
Lateral diamater of pipeline to be installed | in	16
Estimated capital cost		$ 32.1