Summary of Business and Basis of Presentation - Additional Information (Detail) bbl in Billions	9 Months Ended
	Sep. 30, 2015 bbl
Natural Gas Operations [Member]
Summary of Business and Accounting Policies [Line Items]
Annual distribution of natural gas	26.0
Natural gas customers	69,000
Marketing & Production Operations [Member]
Summary of Business and Accounting Policies [Line Items]
Annually market of natural gas	1.3
EWR Subsidiary [Member]
Summary of Business and Accounting Policies [Line Items]
Number of natural gas producing wells and gas gathering assets	160
Gross Percentage Of Working Interest	55.00%
Average Net Revenue Interest, Percentage	46.00%