CONSOLIDATED STATEMENT OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating revenue:
Oil production									$ 761,304	$ 663,958	$ 417,948
Gas production									134,739	170,611	210,686
Natural gas liquids production									48,498	29,996	27,473
Other operational income									3,520	3,938	5,916
Derivative income, net									3,428	1,418	3,265
Total operating revenue	254,871	227,397	226,561	244,957	223,616	214,594	235,734	200,039	951,489	869,921	665,288
Operating expenses:
Lease operating expenses									215,003	175,881	150,212
Transportation, processing and gathering expenses									21,782	8,958	7,218
Production taxes									10,015	9,380	5,808
Depreciation, depletion and amortization									344,365	280,020	248,201
Accretion expense									33,331	30,764	34,469
Salaries, general and administrative expenses									54,648	40,169	42,759
Incentive compensation expense									8,113	11,600	5,888
Other operational expenses									267	2,149	5,579
Total operating expenses									687,524	558,921	500,134
Income from operations	78,397	44,485	56,156	84,927	73,399	80,694	92,155	64,752	263,965	311,000	165,154
Other (income) expenses:
Interest expense									30,375	9,289	12,192
Interest income									(600)	(420)	(1,464)
Other income									(1,805)	(1,942)	(776)
Other expense											671
Loss on early extinguishment of debt									1,972	607	1,820
Total other (income) expenses									29,942	7,534	12,443
Income (loss) before taxes									234,023	303,466	152,711
Provision (benefit) for income taxes:
Current									15,022	(20,386)	5,808
Deferred									69,575	129,520	50,474
Total income taxes									84,597	109,134	56,282
Net income	$ 44,246	$ 23,659	$ 30,547	$ 50,974	$ 45,523	$ 51,821	$ 57,196	$ 39,792	$ 149,426	$ 194,332	$ 96,429
Basic earnings per share	$ 0.89	$ 0.48	$ 0.62	$ 1.03	$ 0.93	$ 1.06	$ 1.17	$ 0.81	$ 3.03	$ 3.97	$ 1.99
Diluted earnings per share	$ 0.89	$ 0.48	$ 0.62	$ 1.03	$ 0.93	$ 1.06	$ 1.17	$ 0.81	$ 3.03	$ 3.97	$ 1.99
Average shares outstanding									48,319	47,988	47,681
Average shares outstanding assuming dilution									48,361	48,030	47,706