Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 12,187	$ 98,511
Restricted cash	0	1,050,015
Accrued production receivable	262,047	253,131
Trade and other receivables, net	78,295	81,971
Derivative assets	5	19,477
Deferred tax assets	52,754	29,156
Other current assets	9,271	10,493
Total current assets	414,559	1,542,754
Oil and natural gas properties (using full cost accounting)
Proved properties	8,945,326	6,963,211
Unevaluated properties	780,481	809,154
CO2 properties	1,117,167	1,032,653
Pipelines and plants	2,209,560	2,035,126
Other property and equipment	466,969	417,207
Less accumulated depletion, depreciation, amortization and impairment	(3,668,225)	(3,180,241)
Net property and equipment	9,851,278	8,077,110
Derivative assets	9,942	36
Goodwill	1,283,590	1,283,590
Other assets	229,368	235,852
Total assets	11,788,737	11,139,342
Current liabilities
Accounts payable and accrued liabilities	410,543	414,668
Oil and gas production payable	174,677	161,945
Derivative liabilities	53,822	2,842
Current maturities of long-term debt	36,157	36,966
Total current liabilities	675,199	616,421
Long-term liabilities
Long-term debt, net of current portion	3,260,625	3,104,462
Asset retirement obligations	119,888	102,730
Derivative liabilities	3,413	23,781
Deferred tax liabilities	2,399,294	2,153,452
Other liabilities	28,912	23,607
Total long-term liabilities	5,812,132	5,408,032
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; 409,215,573 and 406,163,194 shares issued, respectively	409	406
Paid-in capital in excess of par	3,186,714	3,136,461
Retained earnings	2,844,432	2,434,835
Accumulated other comprehensive loss	(276)	(348)
Treasury stock, at cost, 46,710,896 and 30,601,262 shares, respectively	(729,873)	(456,465)
Total stockholders' equity	5,301,406	5,114,889
Total liabilities and stockholders' equity	$ 11,788,737	$ 11,139,342