Acquisitions and Divestitures - Narrative (Details) (USD $)		1 Months Ended
	Nov. 13, 2012	Aug. 31, 2013 Bakken [Member]	Sep. 30, 2012 Bakken [Member]	Sep. 30, 2012 Brazos and Madison Counties [Member]	Jul. 24, 2012 Noble Energy, Inc. [Member]	Sep. 17, 2012 Noble Energy, Inc. [Member] Granite Wash [Member] acre	Sep. 17, 2012 Noble Energy, Inc. [Member] Other Plays [Member] acre	Sep. 17, 2012 Western Oklahoma and Texas Panhandle [Member] Noble Energy, Inc. [Member] acre boe
Business Combination, Description [Abstract]
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				400,000,000
Asset Divestiture [Abstract]
Proceeds from divestiture of assets, net of related expenses		$ 57,100,000	$ 226,600,000	$ 44,100,000