Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 98,511	$ 18,693
Restricted cash	1,050,015	0
Accrued production receivable	253,131	294,689
Trade and other receivables, net	81,971	164,446
Short-term investments	0	86,682
Derivative assets	19,477	47,402
Deferred tax assets	29,156	50,156
Other current assets	10,493	22,045
Total current assets	1,542,754	684,113
Oil and natural gas properties (using full cost accounting)
Proved	6,963,211	7,026,579
Unevaluated	809,154	1,157,106
CO2 properties	1,032,653	596,003
Pipelines and plants	2,035,126	1,701,756
Other property and equipment	417,207	157,674
Less accumulated depletion, depreciation, amortization and impairment	(3,180,241)	(2,627,493)
Net property and equipment	8,077,110	8,011,625
Derivative assets	36	29
Goodwill	1,283,590	1,236,318
Other assets	235,852	252,339
Total assets	11,139,342	10,184,424
Current liabilities
Accounts payable and accrued liabilities	414,668	429,336
Oil and gas production payable	161,945	197,092
Derivative liabilities	2,842	26,523
Current maturities of long-term debt	36,966	8,316
Total current liabilities	616,421	661,267
Long-term liabilities
Long-term debt, net of current portion	3,104,462	2,669,729
Asset retirement obligations	102,730	88,726
Derivative liabilities	23,781	18,872
Deferred taxes	2,153,452	1,918,576
Other liabilities	23,607	20,756
Total long-term liabilities	5,408,032	4,716,659
Commitments and contingencies (Note 11)
Stockholders' equity
Preferred stock, $.001 par value, 25,000,000 shares authorized, none issued and outstanding	0	0
Common stock, $.001 par value, 600,000,000 shares authorized; 406,163,194 and 402,946,070 shares issued, respectively	406	403
Paid-in capital in excess of par	3,136,461	3,090,374
Retained earnings	2,434,835	1,909,475
Accumulated other comprehensive loss	(348)	(418)
Treasury stock, at cost, 30,601,262 and 13,965,673 shares, respectively	(456,465)	(193,336)
Total stockholders' equity	5,114,889	4,806,498
Total liabilities and stockholders' equity	$ 11,139,342	$ 10,184,424