Acquisitions and Divestitures - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended			3 Months Ended					0 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	15 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2012	Jun. 30, 2012	Apr. 24, 2013	Jun. 30, 2013	Apr. 24, 2013	Sep. 30, 2014	Jul. 31, 2014	Aug. 31, 2014
Significant Acquisitions and Disposals
Sale Leaseback Transaction, Deferred Gain, Current	$ 400,000
Sale Leaseback Transaction, Deferred Gain, Net	9,800,000
Business Combination, Consideration Transferred									401,000,000		401,000,000
Payments to Acquire Businesses, Net of Cash Acquired	0	358,239,000	0
Fair value of the Shares issued to seller	0	42,300,000	0
(Gain) loss on sales of assets, net	(120,769,000)	266,000	(4,282,000)
Payments To Settle Obligations Assumed In Acquisition Net	(33,712,000)	22,455,000	0
Eagle Ford Shale, Lavaca County
Significant Acquisitions and Disposals
Asset Acquisition, Purchase Price														45,600,000
Payments to Acquire Oil and Gas Property				34,900,000
Business Combination, Consideration Transferred, Liabilities Incurred				10,700,000
South Texas Oil Gathering Sys. Development Rights
Significant Acquisitions and Disposals
Proceeds from Sale of Intangible Assets				147,100,000
Gain (Loss) on Disposition of Assets				147,100,000
Sale Leaseback Transaction, Recognized Gain, Net				63,000,000
Sale Leaseback Transaction, Deferred Gain, Current	3,400,000
Sale Leaseback Transaction, Deferred Gain, Net	80,700,000
Sale Leaseback Transaction, Deferred Gain, Gross	84,100,000
Selma Chalk, MS Assets
Significant Acquisitions and Disposals
Proceeds from sale of oil and gas property				67,900,000
Impairment of property	117,900,000				117,900,000
South Texas Natural Gas Gathering Assets
Significant Acquisitions and Disposals
Sale Leaseback Transaction, Recognized Gain, Net						56,700,000
Amount of the deferred gain recognized in the current period	400,000
Proceeds from sale of oil and gas property						96,000,000
(Gain) loss on sales of assets, net						(67,300,000)
Appalachia (excluding Marcellus Shale)
Significant Acquisitions and Disposals
Proceeds from sale net transaction costs and closing adjustments							95,700,000
Gain on sale of oil and gas property							3,300,000
Impairment of property								28,600,000
Non-core assets
Significant Acquisitions and Disposals
Proceeds from sale of oil and gas property	2,900,000		1,000,000
Net Payments on Post Closing Adjustments from Property Sales in Prior Years		100,000
(Gain) loss on sales of assets, net	(200,000)		(1,000,000)
Gain (Loss) on Disposition of Property, Plant and Equipment due to Post-close Adjustment		(300,000)
EF Acquisition
Significant Acquisitions and Disposals
Payments to Acquire Businesses, Gross									380,000,000
Oil and gas properties - proved									267,688,000		267,688,000
Oil and gas properties - unproved									119,709,000		119,709,000
Issuance of common stock in acquisition (shares, in millions)									10
PVA common stock price									$ 4.23		$ 4.23
Preferential Purchase Right Settlement										21,000,000
Fair value of receivables acquired									107,345,000		107,345,000
Other assets acquired									2,068,000		2,068,000
Fair value of assets acquired									496,810,000		496,810,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable									94,771,000		94,771,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other									1,500,000		1,500,000
Total liabilities assumed in acquisition									96,271,000		96,271,000
Business Combination, Acquisition Related Costs		2,600,000
Business Combination, Consideration Transferred									400,539,000		400,539,000
Payments to Acquire Businesses, Net of Cash Acquired									358,239,000
Fair value of the Shares issued to seller									42,300,000
Business Combination, Consideration Transferred									400,539,000
Business Combination Purchase Price Adjustments											19,000,000
Payments To Settle Obligations Assumed In Acquisition Net		22,500,000
Disputed Contractual Adjustments, Settled in Arbitration				35,100,000
Arbitration Settlement Interest													1,300,000
Professional fees, post acquisition arbitration proceedings												$ 600,000