Long-Term Debt (Details) (USD $)	1 Months Ended	6 Months Ended			1 Months Ended		6 Months Ended							6 Months Ended								6 Months Ended
	Jul. 31, 2012	Jun. 30, 2012	Aug. 09, 2012	Jul. 30, 2012	Aug. 31, 2012 Revolving Credit Facility [Member]	Jul. 31, 2012 Revolving Credit Facility [Member]	Jun. 30, 2012 Revolving Credit Facility [Member]	Aug. 09, 2012 Revolving Credit Facility [Member]	Jul. 30, 2012 Revolving Credit Facility [Member]	Apr. 11, 2012 Revolving Credit Facility [Member]	Dec. 31, 2011 Revolving Credit Facility [Member]	Jun. 30, 2012 Revolving Credit Facility [Member] Letter of Credit [Member]	Dec. 31, 2011 Revolving Credit Facility [Member] Letter of Credit [Member]	Jun. 30, 2012 Revolving Credit Facility [Member] Minimum [Member]	Jun. 30, 2012 Revolving Credit Facility [Member] Maximum [Member]	Jun. 30, 2011 Senior Notes due 2020 [Member]	Jun. 30, 2012 Interest Rate Option 1 [Member] Revolving Credit Facility [Member]	Jun. 30, 2012 Interest Rate Option 1 [Member] Revolving Credit Facility [Member] Minimum [Member]	Jun. 30, 2012 Interest Rate Option 1 [Member] Revolving Credit Facility [Member] Maximum [Member]	Jun. 30, 2012 Interest Rate Option 2 [Member] Revolving Credit Facility [Member] Minimum [Member]	Jun. 30, 2012 Interest Rate Option 2 [Member] Revolving Credit Facility [Member] Maximum [Member]	Jun. 30, 2012 Forecasted Production In Current Year Attributable To Proved Developed Producing Reserves And Reserves To Be Acquired [Member]	Jun. 30, 2012 Forecasted Production For The Next Two Years From Total Proved Reserves And Total Proved Reserves To Be Acquired [Member]	Jun. 30, 2012 Forecasted Production For Three Plus Years From Total Proved Reserves And Total Proved Reserves To Be Acquired [Member]	Jun. 30, 2012 Bridge Loan [Member]
Credit Agreement, initiation date							Dec. 22, 2010
Credit Agreement, amount outstanding			$ 325,000,000				$ 596,500,000	$ 325,000,000			$ 500,000,000	$ 500,000	$ 400,000
Credit Agreement, remaining borrowing capacity							133,000,000	329,500,000			129,600,000
Credit Agreement, maximum borrowing capacity							1,500,000,000			750,000,000
Credit Agreement, current borrowing capacity							730,000,000		655,000,000	630,000,000
Credit Agreement, expiration date							Apr. 20, 2017
Percentage multiplied by stated principal amount of debt issuance to reduce borrowing base						0.25%
Percentage of oil and gas properties collateralized by liens														80.00%
Interest percentage added to Federal Funds Rate																	0.50%
Interest percentage added to LIBOR Rate																	1.00%
Credit Agreement, interest rate description							Borrowings bear interest at our option of either (i) the greater of the prime rate of Wells Fargo Bank, National Association, the federal funds effective rate plus 0.50%, or the one-month adjusted LIBOR plus 1.0%, all of which would be subject to a margin that varies from 0.50% to 1.50% per annum according to the borrowing base usage (which is the ratio of outstanding borrowings and letters of credit to the borrowing base then in effect), or (ii) the applicable LIBOR plus a margin that varies from 1.50% to 2.50% per annum according to the borrowing base usage.
Credit Agreement, basis spread on variable rate																		0.50%	1.50%	1.50%	2.50%
Credit Agreement, unused portion, commitment fee percentage														0.375%	0.50%
Total debt to EBITDAX ratio to be maintained for Credit Agreement							4.0
Current ratio to be maintained for Credit Agreement							1.0
Percentage of forecasted production prohibiting entering into derivative contracts																						90.00%	85.00%	75.00%
Credit Agreement, reduction in borrowing capacity						75,000,000
Credit Agreement, additional borrowings					20,000,000	20,000,000
Credit Agreement, repayment						291,500,000
Bridge loan, maximum borrowing capacity																									200,000,000
Bridge loan, termination date																									May 10, 2012
Bridge loan, commitment fees																									1,600,000
Senior notes issuance date		Jul. 30, 2012
Senior notes face amount				300,000,000
Senior notes stated interest rate				9.25%
Senior notes, par percentage	98.62%			98.62%
Proceeds from issuance of senior notes	291,200,000
Proceeds from the issuance of senior notes, net of offering costs	290,700,000
Offering costs of senior notes	$ 500,000
Redeemable percentage of aggregate principal amount of debt with proceeds from public or private offering prior to August 15, 2015																35.00%