Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 220,413	$ 35,729
Receivables:
Crude oil and natural gas sales	584,392	468,650
Affiliated parties	15,902	12,410
Joint interest and other, net	339,388	356,111
Derivative assets	76,478	18,389
Inventories	42,085	46,743
Deferred and prepaid taxes	6,425	365
Prepaid expenses and other	8,547	8,386
Total current assets	1,293,630	946,783
Net property and equipment, based on successful efforts method of accounting	9,440,216	8,105,269
Net debt issuance costs and other	74,570	55,726
Noncurrent derivative assets	91,566	32,231
Total assets	10,899,982	9,140,009
Current liabilities:
Accounts payable trade	769,249	687,310
Revenues and royalties payable	276,446	261,856
Payables to affiliated parties	5,476	6,069
Accrued liabilities and other	195,501	153,454
Derivative liabilities	6,809	12,999
Current portion of asset retirement obligations	1,964	2,227
Current portion of long-term debt	1,981	1,950
Total current liabilities	1,257,426	1,125,865
Long-term debt, net of current portion	4,440,820	3,537,771
Other noncurrent liabilities:
Deferred income tax liabilities	1,510,511	1,262,576
Asset retirement obligations, net of current portion	45,568	44,944
Noncurrent derivative liabilities	0	2,173
Other noncurrent liabilities	2,317	2,981
Total other noncurrent liabilities	1,558,396	1,312,674
Commitments and contingencies (Note 7)
Shareholders’ equity:
Preferred stock, $0.01 par value; 25,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.01 par value; 500,000,000 shares authorized; 185,642,832 shares issued and outstanding at June 30, 2013; 185,604,681 shares issued and outstanding at December 31, 2012	1,856	1,856
Additional paid-in capital	1,242,579	1,226,835
Retained earnings	2,398,905	1,935,008
Total shareholders’ equity	3,643,340	3,163,699
Total liabilities and shareholders’ equity	$ 10,899,982	$ 9,140,009