Summary of Significant Accounting Policies (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts Receivable (Textual) [Abstract]
Allowance for doubtful accounts receivable, current	$ 100,000	$ 100,000
Summary of Significant Accounting Policies (Textual) [Abstract]
Total capitalized internal costs	31,100,000	29,300,000	24,600,000
Total capitalized interest cost on unproved properties	7,900,000	7,700,000	7,400,000
Discount rate for estimated future net revenues from proved properties	10.00%
Net gain (loss) related to derivative activities, recognized	2,300,000	(900,000)	700,000
Percentage of working interest in wells	100.00%
Total amount of supervision fees charged to wells	11,300,000	12,900,000	12,500,000
Inventories carried at cost	5,600,000	3,600,000
Inventory Write-down		2,100,000
Liability for Uncertain Tax Positions, Noncurrent	1,000,000
Outstanding checks included in trade accounts payable	13,300,000	18,700,000
Maturity time period for cash and cash equivalents	3 months
Percentage Of Oil And Gas Gross Receipts from Shell Oil Company	46.00%	49.00%	52.00%
Percentage Of Oil And Gas Gross Receipts	11.00%	14.00%
Restricted cash and cash equivalents included in other long term assets	1,000,000	1,300,000
Buyers assumption of asset retirement obligation		27,700,000
Asset Retirement Obligation - current portion	7,134,000	9,279,000
Public stock offering (shares)	0	0	4,038,270
Public Stock Offer Price Per Share			$ 36.60
Proceeds from Issuance of Common Stock			147,800,000
Payments of Stock Issuance Costs			7,700,000
Debt Issuance Costs (Textual) [Abstract]
Reduction of credit facility unamortized issuance costs	700,000
Senior Notes Due Two Thousand Seven Teen [Member]
Debt Issuance Costs (Textual) [Abstract]
Stated Rate of Senior notes	7.125%	7.125%
Balance of issuance costs for credit facility	2,200,000
Senior Notes Due Two Thousand Twenty [Member]
Debt Issuance Costs (Textual) [Abstract]
Stated Rate of Senior notes	8.875%	8.875%
Balance of issuance costs for credit facility	4,000,000
Senior Notes due 2022 [Member]
Debt Issuance Costs (Textual) [Abstract]
Stated Rate of Senior notes	7.875%	7.875%
Balance of issuance costs for credit facility	7,000,000
Line of Credit [Member]
Debt Issuance Costs (Textual) [Abstract]
Balance of issuance costs for credit facility	4,200,000
Maximum [Member]
Summary of Significant Accounting Policies (Textual) [Abstract]
Property, Plant and Equipment, Useful Life		20 years
Minimum [Member]
Summary of Significant Accounting Policies (Textual) [Abstract]
Property, Plant and Equipment, Useful Life	2 years
Trade Accounts Receivable [Member]
Accounts Receivable (Textual) [Abstract]
Trade Accounts Receivable, Gross	53,900,000	58,600,000
Joint Interest Owners [Member]
Accounts Receivable (Textual) [Abstract]
Accounts receivable related to joint interest owners	3,600,000	4,200,000
Other Accounts Receivable [Member]
Accounts Receivable (Textual) [Abstract]
Other Receivables	$ 9,800,000	$ 5,600,000