Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	9 Months Ended												5 Months Ended	12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2014 Cash Flow Hedges [Member]	Jun. 30, 2014 Cash Flow Hedges [Member]	Dec. 31, 2013 Cash Flow Hedges [Member]	Sep. 30, 2013 Cash Flow Hedges [Member]	Jun. 30, 2013 Cash Flow Hedges [Member]	Dec. 31, 2012 Cash Flow Hedges [Member]	Dec. 31, 2014 Scenario, Forecast [Member] Natural Gas [Member] Contract	Dec. 31, 2015 Scenario, Forecast [Member] Natural Gas [Member] Contract
Derivative Instruments, Gain (Loss) [Line Items]
Number of Contracts no longer qualifying as cash flow hedges													3	2
Maximum correlation between price of oil & natural gas in market and underlying price basis indicative in the derivative contract	100.00%
Accumulated other comprehensive income	$ 11,189,000	$ (18,200,000)	$ (2,062,000)	$ 6,400,000	$ 24,500,000	$ 28,800,000	$ 13,200,000	$ (17,800,000)	$ (1,400,000)	$ 6,600,000	$ 25,000,000	$ 28,800,000
Accumulated other comprehensive income, to be reclassified into earnings in the next twelve months	$ 9,300,000