CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income	$ 12,889,000	$ 336,127,000
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on divestiture activity	31,246,000	(245,662,000)
Depletion, depreciation, amortization, and asset retirement obligation liability accretion	523,610,000	343,805,000
Exploratory dry hole expense	18,551,000	49,000
Impairment of proved properties	38,523,000	48,525,000
Abandonment and impairment of unproved properties	11,296,000	4,316,000
Share-based Compensation	21,731,000	19,550,000
Change in Net Profits Plan liability	(17,342,000)	(24,719,000)
Unrealized derivative gain	(7,237,000)	(108,020,000)
Amortization of debt discount and deferred financing costs	5,692,000	14,698,000
Deferred income taxes	7,305,000	164,251,000
Plugging and abandonment	(1,804,000)	(2,935,000)
Other	906,000	(5,952,000)
Changes in current assets and liabilities:
Accounts receivable	(18,682,000)	(20,787,000)
Refundable income taxes	2,339,000	8,482,000
Prepaid expenses and other	(6,203,000)	14,732,000
Accounts payable and accrued expenses	30,766,000	(41,558,000)
Excess income tax benefit from the exercise of stock awards	0	(15,155,000)
Net cash provided by operating activities	653,586,000	489,747,000
Cash flows from investing activities:
Net proceeds from sale of oil and gas properties	48,663,000	325,053,000
Capital expenditures	(1,126,755,000)	(1,081,617,000)
Payments to Acquire Oil and Gas Property	(5,604,000)	0
Other	0	(340,000)
Net cash used in investing activities	(1,083,696,000)	(756,904,000)
Cash flows from financing activities:
Proceeds from credit facility	1,234,500,000	115,500,000
Repayment of credit facility	(1,006,500,000)	(163,500,000)
Debt issuance costs related to credit facility	0	(8,719,000)
Proceeds from Issuance of 6.50% Senior Notes due 2023	392,223,000	0
Proceeds from Issuance of 6.625% Senior Notes	0	341,122,000
Repayments of Convertible Debt	(287,500,000)	0
Proceeds from sale of common stock	3,421,000	5,593,000
Dividends paid	(3,208,000)	(3,181,000)
Payments Related to Tax Withholding for Share-based Compensation	(21,605,000)	(9,967,000)
Excess income tax benefit from the exercise of stock awards	0	15,155,000
Other	(231,000)	0
Net cash provided by (used in) financing activities	311,100,000	292,003,000
Net change in cash and cash equivalents	(119,010,000)	24,846,000
Cash and cash equivalents at beginning of period	119,194,000	5,077,000
Cash and cash equivalents at end of period	184,000	29,923,000
Supplemental schedule of additional cash flow information and noncash investing and financing activities:
Cash paid for interest	(41,413,000)	(24,095,000)
Net cash refunded for income taxes	1,583,000	2,346,000
Dividends, Common Stock	3,300,000	3,200,000
Capital Expenditures Incurred but Not yet Paid	$ 213,600,000	$ 271,500,000