Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets
Cash and cash equivalents	$ 12,046	$ 12,187
Accrued production receivable	287,283	262,047
Trade and other receivables, net	66,001	78,295
Derivative assets	0	5
Deferred tax assets	42,301	52,754
Other current assets	15,342	9,271
Total current assets	422,973	414,559
Oil and natural gas properties (using full cost accounting)
Proved properties	9,374,871	8,945,326
Unevaluated properties	811,935	780,481
CO2 properties	1,142,093	1,117,167
Pipelines and plants	2,225,917	2,209,560
Other property and equipment	465,882	466,969
Less accumulated depletion, depreciation, amortization and impairment	(3,949,275)	(3,668,225)
Net property and equipment	10,071,423	9,851,278
Derivative assets	94	9,942
Goodwill	1,283,590	1,283,590
Other assets	221,597	229,368
Total assets	11,999,677	11,788,737
Current liabilities
Accounts payable and accrued liabilities	342,397	410,543
Oil and gas production payable	172,644	174,677
Derivative liabilities	185,454	53,822
Current maturities of long-term debt	35,533	36,157
Total current liabilities	736,028	675,199
Long-term liabilities
Long-term debt, net of current portion	3,602,156	3,260,625
Asset retirement obligations	119,383	119,888
Derivative liabilities	36,027	3,413
Deferred tax liabilities	2,390,501	2,399,294
Other liabilities	27,636	28,912
Total long-term liabilities	6,175,703	5,812,132
Commitments and contingencies (Note 7)
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; 411,396,702 and 409,215,573 issued, respectively	411	409
Paid-in capital in excess of par	3,213,920	3,186,714
Retained earnings	2,803,876	2,844,432
Accumulated other comprehensive loss	(244)	(276)
Treasury stock, at cost, 59,070,861 and 46,710,896 shares, respectively	(930,017)	(729,873)
Total stockholders' equity	5,087,946	5,301,406
Total liabilities and stockholders' equity	$ 11,999,677	$ 11,788,737