Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 35,729	$ 53,544
Receivables:
Crude oil and natural gas sales	468,650	366,441
Affiliated parties	12,410	31,108
Joint interest and other, net	356,111	379,991
Derivative assets	18,389	6,669
Inventories	46,743	41,270
Deferred and prepaid taxes	365	47,658
Prepaid expenses and other	8,386	9,692
Total current assets	946,783	936,373
Net property and equipment, based on successful efforts method of accounting	8,105,269	4,681,733
Net debt issuance costs and other	55,726	24,355
Noncurrent derivative assets	32,231	3,625
Total assets	9,140,009	5,646,086
Current liabilities:
Accounts payable trade	687,310	642,889
Revenues and royalties payable	261,856	222,027
Payables to affiliated parties	6,069	9,939
Accrued liabilities and other	153,454	117,674
Derivative liabilities	12,999	116,985
Current portion of asset retirement obligations	2,227	2,287
Current portion of long-term debt	1,950
Total current liabilities	1,125,865	1,111,801
Long-term debt, net of current portion	3,537,771	1,254,301
Other noncurrent liabilities:
Deferred income tax liabilities	1,262,576	850,282
Asset retirement obligations, net of current portion	44,944	60,338
Noncurrent derivative liabilities	2,173	57,598
Other noncurrent liabilities	2,981	3,640
Total other noncurrent liabilities	1,312,674	971,858
Commitments and contingencies (Note 10)
Shareholders' equity:
Preferred stock, $0.01 par value; 25,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.01 par value; 500,000,000 shares authorized; 185,604,681 shares issued and outstanding at December 31, 2012; 180,871,688 shares issued and outstanding at December 31, 2011	1,856	1,809
Additional paid-in capital	1,226,835	1,110,694
Retained earnings	1,935,008	1,195,623
Total shareholders' equity	3,163,699	2,308,126
Total liabilities and shareholders' equity	$ 9,140,009	$ 5,646,086