Acquisitions and Divestitures - Additional Information (Detail) (USD $)	1 Months Ended			3 Months Ended				12 Months Ended			1 Months Ended							12 Months Ended			12 Months Ended		1 Months Ended	3 Months Ended	12 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended		1 Months Ended
	Jun. 30, 2012	Jun. 30, 2010	Jan. 31, 2010	Dec. 31, 2012 MBoe	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011 MBoe	Dec. 31, 2012 MBoe	Dec. 31, 2011 MBoe	Dec. 31, 2010 MBoe	Dec. 31, 2011 Counties of Butler and Armstrong in Pennsylvania acre	Apr. 30, 2010 Penn Virginia GP Holdings, L.P. Limited Partner	Dec. 31, 2012 Eagle Ford Shale, Gonzalez and Lavaca Counties acre	Dec. 31, 2012 Eagle Ford Shale acre	Sep. 02, 2012 Eagle Ford Shale Well	Dec. 31, 2011 Eagle Ford Shale acre	Sep. 02, 2012 Eagle Ford Shale Maximum Well	Dec. 31, 2012 Eagle Ford Shale, Gonzales	Dec. 31, 2011 Eagle Ford Shale, Gonzales	Dec. 31, 2010 Eagle Ford Shale, Gonzales	Dec. 31, 2012 Eagle Ford Shale, Lavaca County	Sep. 02, 2012 Eagle Ford Shale, Lavaca County Well	Jul. 31, 2012 Appalachian Region except Marcellus Shale	Jun. 30, 2012 Appalachian Region except Marcellus Shale	Dec. 31, 2012 Appalachian Region except Marcellus Shale	Aug. 31, 2011 Arkoma Divestiture Restructuring	Jun. 30, 2011 Arkoma Divestiture Restructuring	Dec. 31, 2011 Arkoma Divestiture Restructuring	Jul. 02, 2011 Arkoma Divestiture Restructuring acre MMcf	Jan. 31, 2010 Gulf Coast Region	Jan. 31, 2013 Subsequent Event Appalachian Region except Marcellus Shale ft3 Boe
Business Acquisition [Line Items]
AMIAcreage																13,500
Number of wells to be drilled															3		6					17
Current working interest in the acquired acreage																		84.00%			60.00%
Working interest looking for partner																					40.00%
Gas and oil acreage, acquired, net													4,100
Asset acquisition, purchase price													$ 10,000,000						$ 27,000,000	$ 31,000,000
Acquired to date net														32,500
Proceeds from sale of oil and gas property								1,600,000	1,200,000	2,000,000													100,000,000
Proceeds from sale net transaction costs and closing adjustments											8,100,000														95,700,000					23,400,000
Gain on sale of oil and gas property											3,300,000														3,300,000
Production capacity on sold property																															20,000,000
Production capacity on sold property (BOE)																															3,333
Proved reserves of natural gas equivalent sold																													37,100,000,000		106,000,000,000
Proved reserves of BOE				46,980,000			71,562,000	46,980,000	71,562,000	83,587,000																					17,700,000
Gas reserves proved																															96.00%
Gas reserves as a percentage of total reserves																															100.00%
Impairment of property				75,200,000	700,000	28,600,000	33,600,000																	28,600,000			71,000,000	71,100,000
Number of net acres sold											2,700																		73,000
Value of property interests being sold																										30,000,000
Exchange of oil gas and properties			8,200,000
Our reduced limited partner interest in PVG after the sale of units												22.60%
Proceeds from the sale of remaining PVG units, net	139,100,000							0	0	139,120,000
Gain on sale of discontinued operations, net of tax	51,500,000	51,500,000						0	0	51,546,000
Gain on sale of discontinued operations, income tax effects	$ 35,100,000	$ 35,100,000						$ 0	$ 0	$ 35,116,000