Summary of Significant Accounting Policies (Details Textual) (USD $)	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011		Jun. 30, 2010	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable (Textuals) [Abstract]
Accounts receivable	$ 50,146,000		$ 50,146,000			$ 46,975,000
Accounts receivable related to oil and gas sales	45,400,000		45,400,000			43,300,000
Other Receivables	1,400,000		1,400,000			1,400,000
Summary of Significant Accounting Policies (Textuals) [Abstract]
Total capitalized internal costs			14,400,000		11,900,000
Total capitalized interest cost on unproved properties	1,900,000	1,900,000	3,700,000		3,700,000
Estimated useful lives of the property, minimum			2
Estimated useful lives of the property, maximum			20
Discount rate for estimated future net revenues from proved properties	10.00%
Allowance for doubtful accounts receivable, current	100,000		100,000			100,000
Net gain (loss) related to derivative activities, recognized	(800,000)	1,500,000	(1,000,000)		1,000,000
Fair value of derivative instruments	200,000		200,000			300,000
Percentage of working interest interest in wells			100.00%
Total amount of supervision fees charged to wells			6,600,000		6,000,000
Inventories carried at cost	8,700,000		8,700,000			12,800,000
Condition for recognition of income tax benefit being realized upon ultimate settlement with a taxing authority			greater than 50% probability
Unrecognized tax benefits that would impact effective tax rate	1,000,000		1,000,000
Outstanding checks included in trade accounts payable	11,100,000		11,100,000			8,100,000
Maturity time period for cash and cash equivalents			3 months or less
Restricted cash and cash equivalents included in other long term assets	1,300,000		1,300,000			1,300,000
Accumulated other comprehensive loss, net of income tax	200,000		200,000
Tax portion of accumulated other comprehensive loss	100,000		100,000
Total comprehensive income (loss)	41,500,000	11,600,000	61,557,000	[1]	26,900,000	46,379,000
Asset retirement obligation classified as a current liability in accounts payable and accrued liabilities	7,986,000		7,986,000			8,708,000
Public stock offer price per share						$ 36.60
Public stock offering (shares)						4,038,270
Proceeds from Issuance of Common Stock						147,800,000
Payments of stock issuance costs including commissions						7,700,000
Charge related to inventory obsolescence in Price-risk management and other, net			900,000
Natural gas hedges [Member]
Accounts, Notes, Loans and Financing Receivable (Textuals) [Abstract]
Other Receivables	900,000		900,000
Natural Gas Price Floors [Member]
Price-Risk Management Activities (Textual) [Abstract]
Natural Gas production hedged			2,495,000 MMBtu
Natural Gas Price Floors [Member] | Maximum [Member]
Price-Risk Management Activities (Textual) [Abstract]
Strike prices of cover production, $/ Barrel	4.75		4.75
Natural Gas Price Floors [Member] | Minimum [Member]
Price-Risk Management Activities (Textual) [Abstract]
Strike prices of cover production, $/ Barrel	4.55		4.55
Joint interest owners [Member]
Accounts, Notes, Loans and Financing Receivable (Textuals) [Abstract]
Accounts receivable related to joint interest owners	3,400,000		3,400,000			2,300,000
Senior notes due 2017 [Member]
Debt Issuance Costs (Textuals) [Abstract]
Rates of senior notes	7.125%		7.125%
Maturity date of senior notes			Jun. 01, 2017
Balance of issuance costs for credit facility	2,800,000		2,800,000
Net of accumulated amortization	1,400,000		1,400,000
Senior notes due 2020 [Member]
Debt Issuance Costs (Textuals) [Abstract]
Rates of senior notes	8.875%		8.875%
Maturity date of senior notes			Jan. 15, 2020
Balance of issuance costs for credit facility	4,500,000		4,500,000
Net of accumulated amortization	500,000		500,000
Line of Credit [Member]
Debt Issuance Costs (Textuals) [Abstract]
Balance of issuance costs for credit facility	4,000,000		4,000,000
Net of accumulated amortization	$ 3,600,000		$ 3,600,000

[1] [2] Unaudited