Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 8,252	$ 2,812
Accrued production receivable	95,934	100,413
Trade and other receivables, net	87,228	87,924
Derivative assets	72,798	142,846
Other current assets	8,763	10,005
Total current assets	272,975	344,000
Oil and natural gas properties (using full cost accounting)
Proved properties	10,296,792	10,245,195
Unevaluated properties	902,990	894,948
CO2 properties	1,186,607	1,187,458
Pipelines and plants	2,293,102	2,293,219
Other property and equipment	405,039	408,194
Less accumulated depletion, depreciation, amortization and impairment	(9,982,733)	(9,653,205)
Net property and equipment	5,101,797	5,375,809
Other assets	163,775	166,555
Total assets	5,538,547	5,886,364
Current liabilities
Accounts payable and accrued liabilities	186,715	253,197
Oil and gas production payable	79,765	87,337
Derivative liabilities	25,005	0
Current maturities of long-term debt	32,917	32,481
Total current liabilities	324,402	373,015
Long-term liabilities
Long-term debt, net of current portion	3,222,497	3,245,114
Asset retirement obligations	142,101	138,919
Deferred tax liabilities, net	742,148	837,263
Other liabilities	26,121	27,484
Total long-term liabilities	$ 4,132,867	$ 4,248,780
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; 354,340,533 and 354,541,626 shares issued, respectively	354	355
Paid-in capital in excess of par	2,356,069	2,353,134
Accumulated deficit	(1,228,039)	(1,042,882)
Treasury stock, at cost, 3,734,768 and 3,124,311 shares, respectively	(47,106)	(46,038)
Total stockholders' equity	1,081,278	1,264,569
Total liabilities and stockholders' equity	$ 5,538,547	$ 5,886,364