Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income (Loss)	$ 16,433	$ 84,262
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depletion, depreciation and amoritzation	61,468	112,702
Deferred gain on sale of liquids gathering system	(2,640)	0
Deferred Income Tax Provision (Benefit)	0	44,073
Unrealized Gain (Loss) on Derivatives	44,715	(57,746)
Reduction in tax benefits from stock based compensation	0	3,739
Share-based Compensation	3,008	2,456
Other	539	537
Increase (Decrease) in Operating Capital [Abstract]
Increase (Decrease) in Restricted Cash for Operating Activities	2	0
Increase (Decrease) in Accounts Receivable	8,357	49,060
Increase (Decrease) in Prepaid, Deferred Expense and Other Assets	298	(5,698)
Increase (Decrease) in Accounts Payable and Accrued Liabilities	(43,154)	(28,421)
Other long-term obligations	9,238	10,100
Increase (Decrease) in Accrued Income Taxes Payable	(9,282)	(1,646)
Increase (Decrease in Production Taxes Payable	68	(2,586)
Increase (Decrease in Interest Payable	(21,190)	(21,529)
Net Cash Provided by (Used in) Operating Activities	67,860	189,303
Net Cash Provided by (Used in) Investing Activities [Abstract]
Oil and gas property expenditures	(107,395)	(272,241)
Gathering system expenditures	(1,006)	(16,391)
Change in capital cost accrual	(49,420)	(14,139)
Proceeds from Sale of Productive Assets	(27)	0
Inventory	529	(671)
Purchase of Capital Assets	(10)	(1,571)
Net Cash Provided by (Used in) Investing Activities	(157,329)	(305,013)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Proceeds from Issuance of Long-term Debt	314,000	323,000
Repayments of Long-term Debt	(218,000)	(207,000)
Payments for Repurchase of Equity	(5,085)	(5,957)
Reduction in tax benefits from stock based compensation	0	(3,739)
Proceeds from Stock Options Exercised	0	632
Net Cash Provided by (Used in) Financing Activities	90,915	106,936
Cash and Cash Equivalents, Period Increase (Decrease)	1,446	(8,774)
Cash and Cash Equivalents, at Carrying Value	12,921	11,307
Cash and Cash Equivalents, at Carrying Value	14,367	2,533
SUPPLEMENTAL INFORMATION:
Non-cash investing activities - oil and gas properties	$ 12,650	$ 0