Rates and Other Regulatory Activities - Additional Information (Detail) - Eastern Shore [Member] $ in Millions		9 Months Ended	12 Months Ended
	Oct. 13, 2015 dekatherm / d	Sep. 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		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
TETLP Expansion Project [Member]
Rates and Other Regulatory Activities [Line Items]
Volume The Expansion Project Is Expected to Provide	53,000
Total Capacity After Pipeline Improvements	160,000