Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating activities:
Net Income (Loss) Attributable to Parent	$ 453,202	$ 464,459	$ (451,053)
Adjustments to reconcile net (Loss) income to cash provided by operating activities:
Depletion and depreciation	346,394	241,796	201,826
Write-down of proved oil and gas properties	0	0	1,037,000
Deferred and current non-cash income taxes	251,206	253,926	(253,966)
Unrealized loss (gain) on commodity derivatives	(100,383)	(208,625)	92,849
Excess tax benefit from stock based compensation	(6,212)	(17,522)	(14,213)
Stock compensation	13,919	12,944	10,901
Other	1,495	734	1,023
Net changes in operating assets and liabilities:
Restricted cash	(23)	1,583	1,046
Accounts receivable	(26,910)	(31,966)	14,974
Other current assets	(17)	0	2,913
Prepaid expenses and other	(1,291)	(229)	4,268
Other non-current assets	0	(1,176)	(2,905)
Accounts payable, production taxes and accrued liabilities	86,079	91,982	(38,079)
Production taxes payable	8,735	(7,439)	(596)
Interest payable	3,428	14,867	5,902
Other long-term obligations	433	6,035	(13,638)
Taxation payable	3,203	3,359	215
Net cash provided by operating activities	1,033,292	824,728	592,641
Investing Activities:
Acquisition of oil and gas properties	0	(403,806)	0
Oil and gas property expenditures	(1,435,611)	(1,164,389)	(673,518)
Gathering system expenditures	(83,996)	(76,703)	(67,833)
Restricted Cash Non Current	0	28,257	(28,257)
Proceeds on sale of subsidiary, net of transaction costs	5,821	68,420	0
Change in capital cost accrual	125,261	19,826	(56,327)
Inventory	1,595	1,738	4,024
Purchase of property, plant and equipment	(21,865)	(2,442)	1,300
Net cash used in investing activities	(1,408,795)	(1,529,099)	(820,611)
Financing activities:
Borrowings on long-term debt	1,257,000	1,000,000	817,000
Payments on long-term debt	(914,000)	(1,260,000)	(827,000)
Proceeds from issuance of Senior Notes	0	1,025,000	235,000
Deferred financing costs	(6,866)	(4,425)	(1,283)
Repurchased shares/net share settlements	(36,298)	(23,707)	(11,293)
Excess Tax Benefit from Share-based Compensation, Financing Activities	6,212	17,522	14,213
Proceeds from exercise of options	9,928	6,561	1,430
Net cash provided by (used in) financing activities	315,976	760,951	228,067
(Decrease)/increase in cash during the period	(59,527)	56,580	97
Cash and cash equivalents, beginning of period	70,834	14,254	14,157
Cash and cash equivalents, end of period	11,307	70,834	14,254
Cash paid for:
Interest	88,964	53,291	30,579
Income taxes	$ 7,260	$ 2,537	$ 11,403