Acquisitions and Dispositions - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended			1 Months Ended			6 Months Ended		0 Months Ended	1 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 30, 2013	Nov. 30, 2012	Jun. 30, 2014	Jun. 16, 2014	Dec. 31, 2014	Jun. 16, 2014	Apr. 30, 2014
Significant Acquisitions And Disposals [Line Items]
(Loss) gain on the sale of assets	$ 3,760,000	$ 167,000	$ 282,064,000	$ (353,000)	$ 3,162,000	$ 6,008,000	$ 83,287,000	$ (166,000)	$ 285,638,000	$ 92,291,000	$ 49,132,000
Delaware and Permian Basin
Significant Acquisitions And Disposals [Line Items]
(Loss) gain on the sale of assets												83,300,000
Selling expenses for property sale												4,200,000
Proceeds from sale of oil and gas												275,000,000
Ardmore Woodford properties
Significant Acquisitions And Disposals [Line Items]
(Loss) gain on the sale of assets													55,200,000
Proceeds from sale of oil and gas													135,000,000
Miscellaneous Proved and Unproved Properties
Significant Acquisitions And Disposals [Line Items]
(Loss) gain on the sale of assets									2,900,000	13,200,000	(6,100,000)
Nora Gathering, LLC
Significant Acquisitions And Disposals [Line Items]
Percentage of ownership interest, acquired	50.00%								50.00%							50.00%
Percentage ownership interest	50.00%								50.00%							50.00%
Fair value of membership interest on acquisition date									134,800,000
Conger Exchange Transaction
Significant Acquisitions And Disposals [Line Items]
(Loss) gain on the sale of assets			280,100,000
Selling expenses for property sale														5,000,000
Net operating income prior to disposition										48,700,000	40,200,000				21,900,000
Carrying amount of assets prior to exchange																		271,800,000
Recognized revenue from sale of property interests acquired																33,800,000
Net operating income																25,700,000
(Loss) gain on the sale of assets prior to selling expenses														287,700,000
Conger Exchange Transaction | EQT Corporation
Significant Acquisitions And Disposals [Line Items]
Cash proceeds from sale of assets																		145,000,000
Sale and exchange transaction, closing date									Jun. 16, 2014
(Loss) gain on the sale of assets																	272,700,000
Selling expenses for property sale																	5,000,000
Conger Exchange Transaction | Nora Gathering, LLC
Significant Acquisitions And Disposals [Line Items]
Gain on sale of assets									10,000,000
Trade receivables relating to acquisition	5,500,000								5,500,000							5,500,000
Gain on the remeasurement of membership interest														$ 10,000,000