Acquisitions (Narrative) (Details) (USD $)	12 Months Ended		12 Months Ended		12 Months Ended				0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended				0 Months Ended	12 Months Ended					0 Months Ended	12 Months Ended
	Dec. 31, 2012 2011 Notes [Member]	Feb. 14, 2011 2011 Notes [Member]	Dec. 31, 2012 2012 Notes [Member]	Oct. 25, 2012 2012 Notes [Member]	Dec. 31, 2012 Hilcorp Acquisition [Member] MMBoe	Oct. 31, 2012 Hilcorp Acquisition [Member]	Jun. 30, 2012 Hilcorp Acquisition [Member]	Oct. 31, 2012 Hilcorp Acquisition [Member] 2012 Notes [Member]	Mar. 31, 2012 South Timbalier Acquisition [Member] MMBoe	Dec. 31, 2012 South Timbalier Acquisition [Member]	May 15, 2012 South Timbalier Acquisition [Member]	Dec. 31, 2010 ASOP Acquisition [Member] MMBoe	Dec. 31, 2012 ASOP Acquisition [Member]	Dec. 31, 2011 ASOP Acquisition [Member]	Feb. 14, 2012 ASOP Acquisition [Member]	Feb. 14, 2011 ASOP Acquisition [Member]	Nov. 01, 2011 Main Pass Acquisition [Member] MMBoe	Dec. 31, 2012 Main Pass Acquisition [Member]	Dec. 31, 2011 Main Pass Acquisition [Member]	Nov. 17, 2012 Main Pass Acquisition [Member]	Nov. 01, 2012 Main Pass Acquisition [Member]	Dec. 17, 2011 Main Pass Acquisition [Member]	Mar. 05, 2013 Non-Operated Bay Marchand Field Disposition [Member]	Dec. 31, 2012 Non-Operated Bay Marchand Field Disposition [Member]
Business Acquisition [Line Items]
Acquired certain interests in producing oil and natural gas assets		$ 200,700,000				$ 550,000,000					$ 32,400,000				$ 200,700,000	$ 200,700,000				$ 38,600,000		$ 38,600,000
Proved developed reserves, Mmboe					37.2				1.0			8.1					1.3
Percentage of Oil Reserves					49.00%				51.00%			84.00%					96.00%
Percentage of proved developed reserves					58.00%				84.00%			76.00%
Working interest by acquirer prior to acquisition											60.00%
Working interest by acquiree prior to acquisition											40.00%
Senior Notes, face amount	210,000,000	210.0	300.0	300.0				300,000,000							210,000,000
Senior Notes, stated percentage	8.25%		8.25%
Net proceeds from offering of Notes	202,000,000		289,500,000
Economic effective date					Jul. 01, 2012					Apr. 01, 2012			Jan. 01, 2011					Nov. 01, 2011
Purchase Price Adjustments							7,500,000		700,000			3,800,000									700,000
Incurred fees					500,000					100,000				500,000					100,000
Buyers Assumption of Certain Associated Liabilities																							10,800,000
Cash consideration from sale of proptery																							51,500,000
Total consideration from sale of property																							62,300,000
Net book value of property to be sold																								$ 35,600,000