Subsequent Events (Details) (USD $)							0 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 6.625% Senior Subordinated Notes Due 2021 [Member]	May 18, 2011 6.625% Senior Subordinated Notes Due 2021 [Member]	Jun. 30, 2012 Line Of Credit Facility Commitment Amount [Member]	Jun. 30, 2012 Line Of Credit Facility Lender Determined Amount [Member]	Jul. 10, 2012 Agreed Upon Aquisition of Certain Assets [Member] acre	Jul. 10, 2012 Agreed Upon Aquisition of Certain Assets [Member] Line Of Credit Facility Commitment Amount [Member]	Jul. 10, 2012 Agreed Upon Aquisition of Certain Assets [Member] Line Of Credit Facility Lender Determined Amount [Member]	Jul. 12, 2012 Private Offering of Debt [Member]
Subsequent Event [Line Items]
Square footage included in agreed upon assets to be acquired							84,000
Agreed upon cash to be paid to acquire certain oil and natural gas assets from Noble Energy, Inc.							$ 617,100,000
Credit facility current credit amount					250,000,000	600,000,000		750,000,000	800,000,000
Aggregate principal amount										400,000,000
Interest percentage of senior subordinated notes			6.625%	6.625%						6.625%
New Notes sold at percent of par value										98.75%
6.625% senior subordinated notes due 2021	$ 250,000,000	$ 250,000,000		$ 250,000,000
Mandatory redemption price, percent of par										98.75%
Mandatory redemption price, percent of notes being redeemed										99.75%