Acquisitions (Schedule of Revenues and Lease Operating Expenses Attributable to the ST 41 Interests, the ASOP Properties and the Main Pass Interests) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Hilcorp Properties Acquisition [Member]
Business Acquisition [Line Items]
Revenue	$ 37,978
Lease operating expenses	6,711
South Timbalier Acquisition [Member]
Business Acquisition [Line Items]
Revenue	9,262
Lease operating expenses	1,760
ASOP and Main Pass Acquisition [Member]
Business Acquisition [Line Items]
Revenue	175,538	125,975
Lease operating expenses	$ 26,467	$ 17,161