Acquisitions (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended	0 Months Ended			3 Months Ended	6 Months Ended		12 Months Ended		0 Months Ended	6 Months Ended			0 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Feb. 14, 2011 2011 Notes [Member]	Oct. 25, 2012 2012 Notes [Member]	Jun. 30, 2013 2012 Notes [Member]	Jun. 30, 2013 Parent Company [Member]	Jun. 30, 2013 Parent Company [Member]	Jun. 30, 2013 Hilcorp Acquisition [Member]	Dec. 31, 2012 Hilcorp Acquisition [Member] MMBoe	Oct. 31, 2012 Hilcorp Acquisition [Member]	Mar. 31, 2012 South Timbalier Acquisition [Member] MMBoe	Jun. 30, 2013 South Timbalier Acquisition [Member]	May 15, 2012 South Timbalier Acquisition [Member]	Feb. 14, 2011 ASOP Acquisition [Member]	Apr. 02, 2013 Non-Operated Bay Marchand Field Disposition [Member]	Jun. 30, 2013 Non-Operated Bay Marchand Field Disposition [Member]
Business Acquisition [Line Items]
Acquired certain interests in producing oil and natural gas assets										$ 550,000,000			$ 32,400,000	$ 200,700,000
Proved developed reserves, Mmboe									37.2		1.0
Percentage of Oil Reserves									49.00%		51.00%
Percentage of proved developed reserves									58.00%		84.00%
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	300,000,000	300,000,000
Interest Rate, Debt Instrument	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
Purchase Price Adjustments								6,200,000				400,000				1,100,000
Buyers Assumption of Certain Associated Liabilities															11,300,000
Cash consideration from sale of proptery															51,500,000
Total consideration from sale of property															62,800,000
Pre-tax gain on sale of assets	$ 26,856,000	$ 26,856,000				$ 26,394,000	$ 26,394,000									$ 26,400,000