Condensed Consolidating Statement of Operations (Detail) (USD $) In Thousands, 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, amortization									344,365	280,020	248,201
Accretion expense									33,331	30,764	34,469
Salaries, general and administrative									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 (loss) 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 (income) expense, net										(1,942)
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 (loss)	44,246	23,659	30,547	50,974	45,523	51,821	57,196	39,792	149,426	194,332	96,429
Comprehensive income (loss)									156,391	230,404	97,605
Parent
Operating revenue:
Oil production									26,149	5,675	51,357
Gas production									34,331	19,470	61,137
Natural gas liquids production									15,264
Other operational income									2,766	3,085	4,831
Derivative income, net											3,265
Total operating revenue									78,510	28,230	120,590
Operating expenses:
Lease operating expenses									19,914	6,632	64,868
Transportation, processing and gathering expenses									12,049
Production taxes									3,330	1,434	3,631
Depreciation, depletion, amortization									63,022	17,860	40,351
Accretion expense									561	15	14,503
Salaries, general and administrative									54,641	40,073	42,741
Incentive compensation expense									8,113	11,600	5,888
Other operational expenses									173	1,404	2,097
Total operating expenses									161,803	79,018	174,079
Income (loss) from operations									(83,293)	(50,788)	(53,489)
Other (income) expenses:
Interest expense									30,446	9,043	12,192
Interest income									(285)	(178)	(1,439)
Other income									(144)		(53)
Other (income) expense, net										(52)
Other expense											601
Loss on early extinguishment of debt									1,972	607	1,820
(Income) loss from investment in subsidiaries									(223,555)	(232,751)	(140,366)
Total other (income) expenses									(191,566)	(223,331)	(127,245)
Income (loss) before taxes									108,273	172,543	73,756
Provision (benefit) for income taxes:
Current									15,022	(20,386)	5,896
Deferred									(56,175)	(1,403)	(28,569)
Total income taxes									(41,153)	(21,789)	(22,673)
Net income (loss)									149,426	194,332	96,429
Comprehensive income (loss)									156,391	230,404	97,605
Guarantor Subsidiary
Operating revenue:
Oil production									735,155	658,283	366,591
Gas production									100,408	151,141	149,549
Natural gas liquids production									33,234	29,996	27,473
Other operational income									397	249	(54)
Derivative income, net									3,428	1,418
Total operating revenue									872,622	841,087	543,559
Operating expenses:
Lease operating expenses									195,105	169,018	85,344
Transportation, processing and gathering expenses									9,733	8,958	7,218
Production taxes									6,685	7,946	2,177
Depreciation, depletion, amortization									281,152	261,326	206,856
Accretion expense									32,513	30,385	19,524
Salaries, general and administrative									7	94	17
Other operational expenses									94	745	3,482
Total operating expenses									525,289	478,472	324,618
Income (loss) from operations									347,333	362,615	218,941
Other (income) expenses:
Interest expense									(71)	246
Interest income									(315)	(242)	(25)
Other income									(1,661)		(762)
Other (income) expense, net										(1,890)
Other expense											70
(Income) loss from investment in subsidiaries									75	827	337
Total other (income) expenses									(1,972)	(1,059)	(380)
Income (loss) before taxes									349,305	363,674	219,321
Provision (benefit) for income taxes:
Current											(88)
Deferred									125,750	130,923	79,043
Total income taxes									125,750	130,923	78,955
Net income (loss)									223,555	232,751	140,366
Comprehensive income (loss)									223,555	232,751	140,366
Non-Guarantor Subsidiaries
Operating revenue:
Other operational income									357	604	1,139
Total operating revenue									357	604	1,139
Operating expenses:
Lease operating expenses									(16)	231
Depreciation, depletion, amortization									191	834	994
Accretion expense									257	364	442
Salaries, general and administrative										2	1
Total operating expenses									432	1,431	1,437
Income (loss) from operations									(75)	(827)	(298)
Other (income) expenses:
Other income											39
Total other (income) expenses											39
Income (loss) before taxes									(75)	(827)	(337)
Provision (benefit) for income taxes:
Net income (loss)									(75)	(827)	(337)
Comprehensive income (loss)									(75)	(827)	(337)
Eliminations
Other (income) expenses:
(Income) loss from investment in subsidiaries									223,480	231,924	140,029
Total other (income) expenses									223,480	231,924	140,029
Income (loss) before taxes									(223,480)	(231,924)	(140,029)
Provision (benefit) for income taxes:
Net income (loss)									(223,480)	(231,924)	(140,029)
Comprehensive income (loss)									$ (223,480)	$ (231,924)	$ (140,029)