Long-Term Debt (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended
	Jul. 31, 2012	Sep. 30, 2012	Sep. 30, 2012	Nov. 08, 2012	Oct. 30, 2012	Jul. 30, 2012	Apr. 11, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Number of days after fiscal year end to provide audited financial statements for credit agreement			90 days
Number of days after fiscal quarter end to provide unaudited financial statements for credit agreement			45 days
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%
Proceeds from issuance of senior notes	291,200,000
Proceeds from the issuance of senior notes, net of offering costs	290,200,000
Offering costs of senior notes	1,000,000
Redeemable percentage of aggregate principal amount of debt with proceeds from public or private offering prior to August 15, 2015			35.00%
Possible repurchase percentage of principal amount of senior notes			101.00%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit Agreement, initiation date			Dec. 22, 2010
Credit Agreement, amount outstanding		325,000,000	325,000,000	325,000,000				500,000,000
Credit Agreement, remaining borrowing capacity		329,900,000	329,900,000	404,900,000				129,600,000
Credit Agreement, maximum borrowing capacity		1,500,000,000	1,500,000,000				750,000,000
Credit Agreement, current borrowing capacity		730,000,000	730,000,000		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%
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.
Total debt to EBITDAX ratio to be maintained for Credit Agreement			4.0
Current ratio to be maintained for Credit Agreement			1.0
Credit Agreement, reduction in borrowing capacity	75,000,000
Credit Agreement, repayment	291,500,000
Credit Agreement, write-off of deferred loan costs		700,000
Revolving Credit Facility [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Credit Agreement, amount outstanding		100,000	100,000					400,000
Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Percentage of oil and gas properties collateralized by liens			80.00%
Credit Agreement, unused portion, commitment fee percentage			0.375%
Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Credit Agreement, unused portion, commitment fee percentage			0.50%
Interest Rate Option 1 [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Interest percentage added to Federal Funds Rate			0.50%
Interest percentage added to LIBOR Rate			1.00%
Interest Rate Option 1 [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Credit Agreement, basis spread on variable rate		0.50%	0.50%
Interest Rate Option 1 [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Credit Agreement, basis spread on variable rate		1.50%	1.50%
Interest Rate Option 2 [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Credit Agreement, basis spread on variable rate		1.50%	1.50%
Interest Rate Option 2 [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Credit Agreement, basis spread on variable rate		2.50%	2.50%
Forecasted Production In Current Year Attributable To Proved Developed Producing Reserves And Reserves To Be Acquired [Member]
Debt Instrument [Line Items]
Percentage of forecasted production prohibiting entering into derivative contracts			90.00%
Forecasted Production For The Next Two Years From Total Proved Reserves And Total Proved Reserves To Be Acquired [Member]
Debt Instrument [Line Items]
Percentage of forecasted production prohibiting entering into derivative contracts			85.00%
Forecasted Production For Three Plus Years From Total Proved Reserves And Total Proved Reserves To Be Acquired [Member]
Debt Instrument [Line Items]
Percentage of forecasted production prohibiting entering into derivative contracts			75.00%
Bridge Loan [Member]
Debt Instrument [Line Items]
Bridge loan, maximum borrowing capacity			200,000,000
Bridge loan, termination date			May 10, 2012
Bridge loan, commitment fees			$ 1,600,000