Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating activities:
Net Income (Loss) Attributable to Parent	$ (2,176,898)	$ 453,202	$ 464,459
Adjustments to reconcile net (Loss) income to cash provided by operating activities:
Depletion and depreciation	388,985	346,394	241,796
Ceiling test and other impairments	2,972,464	0	0
Deferred and current non-cash income taxes	(712,576)	251,206	253,926
Unrealized loss (gain) on commodity derivatives	230,385	(100,383)	(208,625)
Excess tax benefit from stock based compensation	4,427	(6,212)	(17,522)
Stock compensation	10,756	13,919	12,944
Other	3,667	1,495	734
Net changes in operating assets and liabilities:
Restricted cash	0	(23)	1,583
Accounts receivable	62,758	(26,910)	(31,966)
Prepaid expenses and other	2,066	(1,274)	(229)
Other non-current assets	284	0	(1,176)
Accounts payable and accrued liabilities	(115,597)	86,079	91,982
Production taxes payable	(14,372)	8,735	(7,439)
Interest payable	(213)	3,428	14,867
Other long-term obligations	(9,031)	433	6,035
Current taxes payable	7,720	3,203	3,359
Net cash provided by operating activities	654,825	1,033,292	824,728
Investing Activities:
Acquisition of oil and gas properties	0	0	403,806
Oil and gas property expenditures	(708,017)	(1,435,611)	(1,164,389)
Gathering system expenditures	(127,149)	(83,996)	(76,703)
Restricted Cash Non Current	0	0	28,257
Proceeds on sale of subsidiary, net of transaction costs	0	5,821	68,420
Proceeds from sale of liquids gathering system	203,046	0	0
Proceeds from sale of marketable securities	21,235	0	0
Change in capital cost accrual	38,338	125,261	19,826
Inventory	(374)	1,595	1,738
Purchase of property, plant and equipment	(4,302)	(21,865)	(2,442)
Net cash used in investing activities	(577,223)	(1,408,795)	(1,529,099)
Financing activities:
Borrowings on long-term debt	852,000	1,257,000	1,000,000
Payments on long-term debt	(918,000)	(914,000)	(1,260,000)
Proceeds from issuance of Senior Notes	0	0	1,025,000
Deferred financing costs	0	(6,866)	(4,425)
Repurchased shares/net share settlements	(6,718)	(36,298)	(23,707)
Excess tax benefit from stock based compensation	(4,427)	6,212	17,522
Proceeds from exercise of options	1,157	9,928	6,561
Net cash provided by (used in) financing activities	(75,988)	315,976	760,951
(Decrease)/increase in cash during the period	1,614	(59,527)	56,580
Cash and cash equivalents, beginning of period	11,307	70,834	14,254
Cash and cash equivalents, end of period	12,921	11,307	70,834
Cash paid for:
Interest	101,237	88,964	53,291
Income taxes	$ 4,379	$ 7,260	$ 2,537