Condensed Consolidated Balance Sheets (Unaudited) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Current assets
Cash and cash equivalents	$ 24,363,000	$ 381,869,000
Accrued production receivable	264,999,000	223,584,000
Trade and other receivables, net of allowance	176,734,000	114,149,000
Short-term investments	81,851,000	93,020,000
Derivative assets	116,761,000	24,242,000
Deferred tax assets	0	27,454,000
Total current assets	664,708,000	864,318,000
Oil and natural gas properties (using full cost accounting)
Proved	6,763,404,000	6,042,442,000
Unevaluated	1,088,733,000	870,130,000
CO2 and other non-hydrocarbon gases properties	599,881,000	523,423,000
Pipelines And Plant	1,598,098,000	1,378,239,000
Other property and equipment	142,243,000	120,641,000
Less accumulated depletion, depreciation, amortization, and impairment	2,510,715,000	2,197,517,000
Net property and equipment	7,681,644,000	6,737,358,000
Derivative assets	56,460,000	12,919,000
Goodwill	1,236,094,000	1,232,418,000
Other assets	248,027,000	218,050,000
Total assets	9,886,933,000	9,065,063,000
Current liabilities
Accounts payable and accrued liabilities	405,243,000	350,068,000
Oil and gas production payable	183,521,000	143,145,000
Derivative liabilities	9,253,000	78,184,000
Long-term Debt and Capital Lease Obligations, Current	8,177,000	7,948,000
Deferred Tax Liabilities, Current	37,326,000	0
Total current liabilities	643,520,000	579,345,000
Long-term liabilities
Long-term debt, net of current portion	2,396,549,000	2,416,208,000
Asset retirement obligations	87,725,000	81,290,000
Derivative liabilities	732,000	29,687,000
Deferred taxes	1,799,793,000	1,547,992,000
Other Liabilities, Noncurrent	22,842,000	29,834,000
Total long-term liabilities	4,307,641,000	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	3,085,862,000	3,045,937,000
Retained earnings	1,856,868,000	1,336,142,000
Accumulated other comprehensive income (loss)	(7,361,000)	(488,000)
Treasury stock, at cost	0	(1,284,000)
Total stockholders' equity	4,935,772,000	4,380,707,000
Total liabilities and stockholders' equity	$ 9,886,933,000	$ 9,065,063,000