Long-Term Debt (Details) (USD $)	3 Months Ended			6 Months Ended								3 Months Ended				3 Months Ended			6 Months Ended					3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011	Dec. 31, 2011		May 31, 2011	May 31, 2012 Before Increase [Member]	Jun. 30, 2012 After Increase [Member]	Jun. 30, 2012 Bank Borrowings [Member]	Jun. 30, 2012 Bank Borrowings [Member] Before Increase [Member] Banks	May 31, 2011 Bank Borrowings [Member] Before Increase [Member]	May 31, 2011 Bank Borrowings [Member] After Increase [Member]	Jun. 30, 2012 Senior notes due 2020 [Member]		Jun. 30, 2011 Senior notes due 2020 [Member]	Jun. 30, 2012 Senior notes due 2020 [Member]		Jun. 30, 2011 Senior notes due 2020 [Member]	Dec. 31, 2011 Senior notes due 2020 [Member]		Jun. 30, 2012 Senior notes due 2017 [Member]	Jun. 30, 2011 Senior notes due 2017 [Member]	Jun. 30, 2012 Senior notes due 2017 [Member]	Jun. 30, 2011 Senior notes due 2017 [Member]	Dec. 31, 2011 Senior notes due 2017 [Member]	Jun. 30, 2012 Senior Notes Due 2022 [Member]		Jun. 30, 2012 Senior Notes Due 2022 [Member]		Dec. 31, 2011 Senior Notes Due 2022 [Member]		Jun. 30, 2012 Line of Credit [Member]	Jun. 30, 2011 Line of Credit [Member]	Jun. 30, 2012 Line of Credit [Member]	Jun. 30, 2011 Line of Credit [Member]	Jun. 30, 2012 Senior Notes Due Two Thousand Twenty Two [Member]
Debt Instrument [Line Items]
Allowance for Doubtful Accounts Receivable, Current	$ 100,000			$ 100,000			$ 100,000
Long-term debt
Long-Term Debt	719,977,000	[1]		719,977,000	[1]		719,775,000	[1]								222,007,000	[1]		222,007,000	[1]		221,873,000	[1]	250,000,000		250,000,000		250,000,000	247,970,000	[1]	247,970,000	[1]	247,902,000	[1]
Long Term Debt (Textual) [Abstract]
Senior notes, issued																225,000,000			225,000,000					250,000,000		250,000,000			250,000,000		250,000,000								250,000,000
Maximum availability aggregate facility amount														500,000,000	700,000,000
Borrowing base										375,000,000	375,000,000
Percentage of applicable margin with federal fund rate												0.50%
Percentage of applicable margin with LIBOR												1.00%
Minimum Debt Instrument Escalating Basis Spread on Base Rate												50
Maximum escalating rates on applicable margins depending upon outstanding debt												150
Minimum escalating rates for Eurodollar rate loans												150
Maximum escalating rates for Eurodollar rate loans												250
Interest expense including commitment fees and amortization of debt issuance costs relating to the credit facility	13,319,000		8,622,000	26,784,000		17,010,000										5,200,000		5,100,000	10,300,000		10,300,000			4,600,000	4,500,000	9,100,000	9,100,000		5,000,000		10,100,000				600,000	600,000	1,200,000	1,200,000
Stated Rate of Senior notes																8.875%			8.875%					7.125%		7.125%			7.875%		7.875%
Percentage at which senior notes are issued, of par value																98.389%			98.389%					100.00%		100.00%			99.156%		99.156%
Effective Interest Rate On Senior Notes Including Discount																9.125%			9.125%										8.00%		8.00%
Unamortized issuance discount on senior notes due 2022																3,600,000			3,600,000										2,100,000		2,100,000
Redemption price plus accrued and unpaid interest																104.438%								103.563%					103.938%
Redemption price, plus accrued and unpaid interest declining in twelve-month intervals																100.00%								100.00%					100.00%
Percentage of maximum redemption of principal amount of notes																			35.00%												35.00%
Redemption of Debts with Net Proceeds of Qualifying Offerings at Price Above Principle Amount of Debts																108.875%													107.875%
Initial Debt Issuance Costs Capitalized																5,000,000			5,000,000					4,200,000		4,200,000													4,800,000
Holder right to require company to repurchase notes at purchase price in cash																			101.00%							101.00%					101.00%
Long Term Debt (Additional Textual) [Abstract]
Capitalized interest on our unproved properties	2,000,000		1,900,000	4,000,000		3,700,000
Number of syndicated banks													10
Addition Line of Credit Facility Maximum Borrowing Capacity									200,000,000
Current Borrowing base										375,000,000	375,000,000
Current Committed borrowing base amount										300,000,000	300,000,000
Amount outstanding under credit facility	0			0			0
Lead bank's prime rate	3.25%			3.25%
Commitment Fee Basis Points On Unused Line of Credit Facility	50			50
Maximum level of cash dividends in any fiscal year	15,000,000			15,000,000
Aggregate limitation on purchases of stock	50,000,000			50,000,000
Commitment fees included in interest expense, net																																			$ 400,000	$ 400,000	$ 700,000	$ 700,000

[1] Amounts are shown net of debt discount