Condensed Consolidated Balance Sheets (Unaudited) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Current assets
Cash and cash equivalents	$ 121,792,000	$ 381,869,000
Accrued production receivable	255,034,000	223,584,000
Trade and other receivables, net of allowance	153,018,000	114,149,000
Short-term investments	88,220,000	93,020,000
Derivative assets	19,322,000	24,242,000
Deferred tax assets	22,097,000	27,454,000
Total current assets	659,483,000	864,318,000
Oil and natural gas properties (using full cost accounting)
Proved	6,508,928,000	6,042,442,000
Unevaluated	952,452,000	870,130,000
CO2 and other non-hydrocarbon gases properties	572,957,000	523,423,000
Pipelines And Plant	1,445,214,000	1,378,239,000
Other property and equipment	138,671,000	120,641,000
Less accumulated depletion, depreciation, amortization, and impairment	2,403,741,000	2,197,517,000
Net property and equipment	7,214,481,000	6,737,358,000
Derivative assets	17,609,000	12,919,000
Goodwill	1,232,418,000	1,232,418,000
Other assets	215,432,000	218,050,000
Total assets	9,339,423,000	9,065,063,000
Current liabilities
Accounts payable and accrued liabilities	333,953,000	345,998,000
Oil and gas production payable	172,837,000	143,145,000
Derivative liabilities	81,627,000	78,184,000
Less current obligations	8,622,000	7,948,000
Other Liabilities, Current	4,070,000	4,070,000
Total current liabilities	601,109,000	579,345,000
Long-term liabilities
Long-term debt, net of current portion	2,288,112,000	2,416,208,000
Asset retirement obligations	86,109,000	81,290,000
Derivative liabilities	3,378,000	29,687,000
Deferred taxes	1,687,839,000	1,547,992,000
Other Liabilities, Noncurrent	24,562,000	29,834,000
Total long-term liabilities	4,090,000,000	4,105,011,000
Stockholders' equity
Preferred Stock, Value, Issued	0	0
Common Stock, Value, Issued	403,000	400,000
Paid-in capital in excess of par	3,074,335,000	3,045,937,000
Retained earnings	1,581,198,000	1,336,142,000
Accumulated other comprehensive income (loss)	(3,429,000)	(488,000)
Treasury stock, at cost	(4,193,000)	(1,284,000)
Total stockholders' equity	4,648,314,000	4,380,707,000
Total liabilities and stockholders' equity	$ 9,339,423,000	$ 9,065,063,000