Acquisitions and Divestitures - Narrative (Details) (USD $)	3 Months Ended								12 Months Ended					1 Months Ended			3 Months Ended				1 Months Ended
	Dec. 31, 2013 rig	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 rig	Dec. 31, 2012	Dec. 31, 2011	Nov. 13, 2012	May 18, 2011	Aug. 31, 2013 Bakken [Member]	Sep. 30, 2012 Bakken [Member]	Sep. 30, 2012 Brazos and Madison Counties [Member]	Dec. 31, 2012 Noble Energy, Inc. [Member]	Jul. 24, 2012 Noble Energy, Inc. [Member]	Sep. 17, 2012 Noble Energy, Inc. [Member] Granite Wash [Member] locations acre	Sep. 17, 2012 Noble Energy, Inc. [Member] Other Plays [Member] acre	Jul. 20, 2011 Oklahoma And Lipscomb [Member] acre Unit	Aug. 31, 2011 Oklahoma Arkoma Woodford And Hartshorne Coal [Member] locations	Aug. 31, 2012 Oklahoma Arkoma Woodford And Hartshorne Coal [Member] acre	Sep. 17, 2012 Western Oklahoma and Texas Panhandle [Member] Noble Energy, Inc. [Member] systems MMBoe acre
Business Combination, Description [Abstract]
Payments to acquire oil and gas property																					$ 12,300,000	$ 30,500,000
Acquired operated wells																					30
Acquired non-operated wells																					59
Purchase price allocation for proved properties																					8,400,000
Unproved properties																					3,900,000
Acres acquired held by production																					12,000
Operating and non-operating number of wells																						500
Oil And Gas Developed And Undeveloped Acreage Net																							55,000
Percentage of acre held for production																						96.00%
Land acquired (in acres)																			24,000	59,000				83,000
Total consideration given																								592,627,000
Proved developed reserves (BOE)																								44,000,000
Number of horizontal driling locations included in the land acquired																			600
Acquired land with existing production capacity, percent																				95.00%
Natural gas gathering systems received as part of acquisition																								4
Aggregate principal amount												650,000,000	250,000,000					400,000,000
Revenues	359,121,000	333,776,000	340,421,000	318,532,000	331,582,000	321,790,000	327,785,000	333,966,000	1,351,850,000	1,315,123,000	1,207,503,000						21,400,000
Net income	51,301,000	34,232,000	59,007,000	40,206,000	(56,547,000)	46,586,000	(19,302,000)	52,439,000	184,746,000	23,176,000	195,867,000						800,000
Asset Divestiture [Abstract]
Proceeds from divestiture of assets									21,700,000					57,100,000	226,600,000	44,100,000
Number of rigs sold									5
Gain (Loss) on Disposition of Property Plant Equipment									16,500,000
Number of rigs held for sale	4								4
Assets held for sale	15,621,000				0				15,621,000	0
Estimated gain (loss) on sale of assets									$ 10,400,000