Condensed Consolidating Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Oil production	$ 180,806	$ 157,436	$ 564,745	$ 484,788
Gas production	34,003	42,771	91,006	131,815
Natural gas liquids production	11,910	9,060	35,228	25,290
Other operational income	678	1,245	2,520	2,994
Total operating revenue	227,397	214,594	696,618	648,187
Lease operating expenses	60,995	46,591	157,030	130,486
Transportation, processing and gathering expenses	6,762	2,763	15,911	7,311
Other operational expenses	82	654	195	1,452
Production taxes	1,842	2,492	7,578	6,828
Depreciation, depletion, amortization	89,274	64,462	260,982	204,777
Accretion expense	8,405	7,700	24,926	23,134
Salaries, general and administrative	13,673	7,151	40,521	29,494
Incentive compensation expense	67	2,087	3,907	7,104
Derivative expense, net	(1,812)	4,082	3,119	3,300
Total operating expenses	182,912	133,900	511,050	410,586
Income (loss) from operations	44,485	80,694	185,568	237,601
Interest expense	7,692	1,379	21,107	6,470
Interest income	(117)	(23)	(227)	(170)
Other income	(443)	(372)	(1,229)	(1,499)
Total other (income) expenses	7,132	1,292	19,651	5,909
Income (loss) before taxes	37,353	79,402	165,917	231,692
Current	595	(12,681)	1,164	(15,043)
Deferred	13,099	40,262	59,573	97,926
Total income taxes	13,694	27,581	60,737	82,883
Net income (loss)	23,659	51,821	105,180	148,809
Comprehensive income (loss)	(9,507)	127,828	113,151	228,454
Other expense		308		501
Loss on early extinguishment of debt				607
Parent
Oil production	7,682	1,248	20,729	2,766
Gas production	9,197	6,772	20,693	12,355
Natural gas liquids production	5,436		11,010
Other operational income	568	1,050	2,024	2,359
Total operating revenue	22,883	9,070	54,456	17,480
Lease operating expenses	5,886	1,716	17,108	2,462
Transportation, processing and gathering expenses	4,163		8,361
Other operational expenses	61	622	150	715
Production taxes	684	422	2,354	814
Depreciation, depletion, amortization	19,336	5,615	45,884	11,533
Accretion expense	138	3	423	11
Salaries, general and administrative	13,672	7,193	40,516	29,486
Incentive compensation expense	67	2,087	3,907	7,104
Total operating expenses	44,007	17,658	118,703	52,125
Income (loss) from operations	(21,124)	(8,588)	(64,247)	(34,645)
Interest expense	7,671	1,305	21,189	6,315
Interest income	(112)	(23)	(216)	(164)
Other income	(98)	(6)	(121)	(19)
(Income) loss from investment in subsidiaries	(42,200)	(60,498)	(160,650)	(177,442)
Total other (income) expenses	(34,739)	(58,914)	(139,798)	(170,203)
Income (loss) before taxes	13,615	50,326	75,551	135,558
Current	595	(12,681)	1,164	(12,690)
Deferred	(10,639)	11,186	(30,793)	(561)
Total income taxes	(10,044)	(1,495)	(29,629)	(13,251)
Net income (loss)	23,659	51,821	105,180	148,809
Comprehensive income (loss)	(9,507)	127,828	113,151	228,454
Other expense		308		500
Loss on early extinguishment of debt				607
Guarantor Subsidiary
Oil production	173,124	156,188	544,016	482,022
Gas production	24,806	35,999	70,313	119,460
Natural gas liquids production	6,474	9,060	24,218	25,290
Other operational income	(1)	94	139	179
Total operating revenue	204,403	205,423	641,805	630,251
Lease operating expenses	55,107	44,682	139,937	127,831
Transportation, processing and gathering expenses	2,599	2,763	7,550	7,311
Other operational expenses	21	32	45	734
Production taxes	1,158	2,070	5,224	6,014
Depreciation, depletion, amortization	69,939	58,630	214,908	192,566
Accretion expense	8,181	7,605	24,246	22,849
Salaries, general and administrative	1	(43)	5	7
Derivative expense, net	(1,812)	4,082	3,119	3,300
Total operating expenses	138,818	115,739	391,915	357,312
Income (loss) from operations	65,585	89,684	249,890	272,939
Interest expense	21	74	(82)	155
Interest income	(5)		(11)	(6)
Other income	(345)	(366)	(1,108)	(1,480)
(Income) loss from investment in subsidiaries	(24)	401	75	692
Total other (income) expenses	(353)	109	(1,126)	(638)
Income (loss) before taxes	65,938	89,575	251,016	273,577
Current				(2,353)
Deferred	23,738	29,076	90,366	98,487
Total income taxes	23,738	29,076	90,366	96,134
Net income (loss)	42,200	60,499	160,650	177,443
Comprehensive income (loss)	42,200	60,499	160,650	177,443
Other expense				1
Non-Guarantor Subsidiaries
Other operational income	111	101	357	456
Total operating revenue	111	101	357	456
Lease operating expenses	2	193	(15)	193
Other operational expenses				3
Depreciation, depletion, amortization	(1)	217	190	678
Accretion expense	86	92	257	274
Salaries, general and administrative		1		1
Total operating expenses	87	503	432	1,149
Income (loss) from operations	24	(402)	(75)	(693)
Income (loss) before taxes	24	(402)	(75)	(693)
Net income (loss)	24		(75)	(693)
Comprehensive income (loss)	24		(75)	(693)
Eliminations
(Income) loss from investment in subsidiaries	42,224	60,097	160,575	176,750
Total other (income) expenses	42,224	60,097	160,575	176,750
Income (loss) before taxes	(42,224)	(60,097)	(160,575)	(176,750)
Net income (loss)	(42,224)		(160,575)	(176,750)
Comprehensive income (loss)	$ (42,224)		$ (160,575)	$ (176,750)