Condensed Consolidating Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating revenue:
Oil production	$ 186,608	$ 180,806	$ 558,031	$ 564,745
Gas production	52,728	34,003	137,382	91,006
Natural gas liquids production	16,476	11,910	36,854	35,228
Other operational income	873	678	2,659	2,520
Derivative income, net				3,119
Total operating revenue	256,685	227,397	734,926	696,618
Operating expenses:
Lease operating expenses	53,986	60,995	157,547	157,030
Transportation, processing and gathering expenses	13,081	6,762	27,374	15,911
Production taxes	5,224	1,842	11,404	7,578
Depreciation, depletion, amortization	92,853	89,274	255,497	260,982
Accretion expense	8,431	8,405	25,012	24,926
Salaries, general and administrative	14,201	13,673	43,351	40,521
Incentive compensation expense	4,566	67	8,047	3,907
Other operational expenses	237	82	382	195
Derivative expense, net	1,684	1,812	1,537
Total operating expenses	194,263	182,912	530,151	511,050
Income (loss) from operations	62,422	44,485	204,775	185,568
Other (income) expenses:
Interest expense	7,922	7,692	26,452	21,107
Interest income	(1,311)	(117)	(1,543)	(227)
Other income	(782)	(443)	(2,190)	(1,229)
(Income) loss from investment in subsidiaries
Total other (income) expenses	5,829	7,132	22,719	19,651
Income (loss) before taxes	56,593	37,353	182,056	165,917
Provision (benefit) for income taxes:
Current	(88)	595	(10,827)	1,164
Deferred	20,579	13,099	77,001	59,573
Total income taxes	20,491	13,694	66,174	60,737
Net income	36,102	23,659	115,882	105,180
Comprehensive income (loss)	17,985	(9,507)	93,462	113,151
Parent [Member]
Operating revenue:
Oil production	6,904	7,682	20,625	20,729
Gas production	19,971	9,197	47,240	20,693
Natural gas liquids production	9,224	5,436	17,901	11,010
Other operational income	711	568	2,150	2,024
Total operating revenue	36,810	22,883	87,916	54,456
Operating expenses:
Lease operating expenses	3,895	5,886	9,611	17,108
Transportation, processing and gathering expenses	10,072	4,163	17,853	8,361
Production taxes	1,773	684	3,960	2,354
Depreciation, depletion, amortization	26,728	19,336	62,007	45,884
Accretion expense	93	138	279	423
Salaries, general and administrative	14,202	13,672	43,300	40,516
Incentive compensation expense	4,566	67	8,047	3,907
Other operational expenses	194	61	295	150
Derivative expense, net
Total operating expenses	61,523	44,007	145,352	118,703
Income (loss) from operations	(24,713)	(21,124)	(57,436)	(64,247)
Other (income) expenses:
Interest expense	7,922	7,671	26,431	21,189
Interest income	(1,234)	(112)	(1,384)	(216)
Other income	(230)	(98)	(671)	(121)
(Income) loss from investment in subsidiaries	(56,166)	(42,200)	(168,887)	(160,650)
Total other (income) expenses	(49,708)	(34,739)	(144,511)	(139,798)
Income (loss) before taxes	24,995	13,615	87,075	75,551
Provision (benefit) for income taxes:
Current	(88)	595	(10,827)	1,164
Deferred	(11,019)	(10,639)	(17,980)	(30,793)
Total income taxes	(11,107)	(10,044)	(28,807)	(29,629)
Net income	36,102	23,659	115,882	105,180
Comprehensive income (loss)	17,985	(9,507)	93,462	113,151
Guarantor Subsidiary [Member]
Operating revenue:
Oil production	179,704	173,124	537,406	544,016
Gas production	32,757	24,806	90,142	70,313
Natural gas liquids production	7,252	6,474	18,953	24,218
Other operational income	162	(1)	509	139
Derivative income, net				3,119
Total operating revenue	219,875	204,403	647,010	641,805
Operating expenses:
Lease operating expenses	50,091	55,107	147,936	139,937
Transportation, processing and gathering expenses	3,009	2,599	9,521	7,550
Production taxes	3,451	1,158	7,444	5,224
Depreciation, depletion, amortization	66,125	69,939	193,490	214,908
Accretion expense	8,338	8,181	24,733	24,246
Salaries, general and administrative		1	4	5
Incentive compensation expense
Other operational expenses	43	21	87	45
Derivative expense, net	1,684	1,812	1,537
Total operating expenses	132,741	138,818	384,752	391,915
Income (loss) from operations	87,134	65,585	262,258	249,890
Other (income) expenses:
Interest expense		21	21	(82)
Interest income	(69)	(5)	(144)	(11)
Other income	(552)	(345)	(1,519)	(1,108)
(Income) loss from investment in subsidiaries		(24)		75
Total other (income) expenses	(621)	(353)	(1,642)	(1,126)
Income (loss) before taxes	87,755	65,938	263,900	251,016
Provision (benefit) for income taxes:
Current
Deferred	31,598	23,738	94,981	90,366
Total income taxes	31,598	23,738	94,981	90,366
Net income	56,157	42,200	168,919	160,650
Comprehensive income (loss)	56,157	42,200	168,919	160,650
Non-Guarantor Subsidiaries [Member]
Operating revenue:
Other operational income		111		357
Total operating revenue		111		357
Operating expenses:
Lease operating expenses		2		(15)
Depreciation, depletion, amortization		(1)		190
Accretion expense		86		257
Salaries, general and administrative	(1)		47
Total operating expenses	(1)	87	47	432
Income (loss) from operations	1	24	(47)	(75)
Other (income) expenses:
Interest income	(8)		(15)
(Income) loss from investment in subsidiaries	(7)		32
Total other (income) expenses	(15)		17
Income (loss) before taxes	16	24	(64)	(75)
Provision (benefit) for income taxes:
Net income	16	24	(64)	(75)
Comprehensive income (loss)	16	24	(64)	(75)
Eliminations [Member]
Other (income) expenses:
(Income) loss from investment in subsidiaries	56,173	42,224	168,855	160,575
Total other (income) expenses	56,173	42,224	168,855	160,575
Income (loss) before taxes	(56,173)	(42,224)	(168,855)	(160,575)
Provision (benefit) for income taxes:
Net income	(56,173)	(42,224)	(168,855)	(160,575)
Comprehensive income (loss)	$ (56,173)	$ (42,224)	$ (168,855)	$ (160,575)