Condensed Consolidating Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating revenue:
Oil production	$ 184,498	$ 182,181	$ 371,423	$ 383,939
Gas production	47,832	28,146	84,654	57,003
Natural gas liquids production	11,200	9,866	20,378	23,318
Other operational income	979	952	1,786	1,842
Derivative income, net	1,368	5,416	147	4,931
Total operating revenue	245,877	226,561	478,388	471,033
Operating expenses:
Lease operating expenses	50,517	51,555	103,561	96,035
Transportation, processing and gathering expenses	8,896	5,492	14,293	9,149
Production taxes	4,091	2,358	6,180	5,736
Depreciation, depletion, amortization	87,209	87,133	162,644	171,708
Accretion expense	8,318	8,255	16,581	16,521
Salaries, general and administrative	15,198	13,143	29,150	26,848
Incentive compensation expense	2,050	2,398	3,481	3,840
Other operational expenses	73	71	145	113
Total operating expenses	176,352	170,405	336,035	329,950
Income (loss) from operations	69,525	56,156	142,353	141,083
Other (income) expenses:
Interest expense	8,895	7,684	18,530	13,415
Interest income	(115)	(79)	(232)	(110)
Other income	(682)	(366)	(1,408)	(786)
Total other (income) expenses	8,098	7,239	16,890	12,519
Income (loss) before taxes	61,427	48,917	125,463	128,564
Provision (benefit) for income taxes:
Current	(6,993)	(665)	(10,739)	569
Deferred	29,398	19,035	56,422	46,474
Total income taxes	22,405	18,370	45,683	47,043
Net income	39,022	30,547	79,780	81,521
Comprehensive income	53,060	93,749	75,477	122,658
Parent
Operating revenue:
Oil production	8,378	6,813	13,721	13,047
Gas production	20,071	5,865	27,269	11,496
Natural gas liquids production	6,378	1,710	8,677	5,574
Other operational income	790	762	1,439	1,456
Total operating revenue	35,617	15,150	51,106	31,573
Operating expenses:
Lease operating expenses	3,425	6,318	5,716	11,222
Transportation, processing and gathering expenses	5,729	1,710	7,781	4,198
Production taxes	1,320	507	2,187	1,670
Depreciation, depletion, amortization	25,088	15,071	35,279	26,548
Accretion expense	93	137	186	285
Salaries, general and administrative	15,150	14,190	29,098	26,844
Incentive compensation expense	2,050	2,398	3,481	3,840
Other operational expenses	51	47	101	89
Total operating expenses	52,906	40,378	83,829	74,696
Income (loss) from operations	(17,289)	(25,228)	(32,723)	(43,123)
Other (income) expenses:
Interest expense	8,882	7,672	18,509	13,518
Interest income	(70)	(74)	(150)	(104)
Other income	(217)	(4)	(441)	(23)
(Income) from investment in subsidiaries	(55,893)	(52,313)	(112,721)	(118,450)
Total other (income) expenses	(47,298)	(44,719)	(94,803)	(105,059)
Income (loss) before taxes	30,009	19,491	62,080	61,936
Provision (benefit) for income taxes:
Current	(6,993)	(665)	(10,739)	569
Deferred	(2,020)	(10,391)	(6,961)	(20,154)
Total income taxes	(9,013)	(11,056)	(17,700)	(19,585)
Net income	39,022	30,547	79,780	81,521
Comprehensive income	53,060	93,749	75,477	122,658
Guarantor Subsidiary
Operating revenue:
Oil production	176,120	175,368	357,702	370,892
Gas production	27,761	22,281	57,385	45,507
Natural gas liquids production	4,822	8,156	11,701	17,744
Other operational income	189	77	347	140
Derivative income, net	1,368	5,416	147	4,931
Total operating revenue	210,260	211,298	427,282	439,214
Operating expenses:
Lease operating expenses	47,092	45,443	97,845	84,830
Transportation, processing and gathering expenses	3,167	3,782	6,512	4,951
Production taxes	2,771	1,851	3,993	4,066
Depreciation, depletion, amortization	62,121	71,969	127,365	144,969
Accretion expense	8,225	8,033	16,395	16,065
Salaries, general and administrative		(1,047)	4	4
Other operational expenses	22	24	44	24
Total operating expenses	123,398	130,055	252,158	254,909
Income (loss) from operations	86,862	81,243	175,124	184,305
Other (income) expenses:
Interest expense	13	12	21	(103)
Interest income	(38)	(5)	(75)	(6)
Other income	(465)	(362)	(967)	(763)
(Income) from investment in subsidiaries		(140)		99
Total other (income) expenses	(490)	(495)	(1,021)	(773)
Income (loss) before taxes	87,352	81,738	176,145	185,078
Provision (benefit) for income taxes:
Deferred	31,418	29,426	63,383	66,628
Total income taxes	31,418	29,426	63,383	66,628
Net income	55,934	52,312	112,762	118,450
Comprehensive income	55,934	52,312	112,762	118,450
Non-Guarantor Subsidiaries
Operating revenue:
Other operational income		113		246
Total operating revenue		113		246
Operating expenses:
Lease operating expenses		(206)		(17)
Depreciation, depletion, amortization		93		191
Accretion expense		85		171
Salaries, general and administrative	48		48
Total operating expenses	48	(28)	48	345
Income (loss) from operations	(48)	141	(48)	(99)
Other (income) expenses:
Interest income	(7)		(7)
(Income) from investment in subsidiaries	39		39
Total other (income) expenses	32		32
Income (loss) before taxes	(80)	141	(80)	(99)
Provision (benefit) for income taxes:
Net income	(80)	141	(80)	(99)
Comprehensive income	(80)	141	(80)	(99)
Eliminations
Other (income) expenses:
(Income) from investment in subsidiaries	55,854	52,453	112,682	118,351
Total other (income) expenses	55,854	52,453	112,682	118,351
Income (loss) before taxes	(55,854)	(52,453)	(112,682)	(118,351)
Provision (benefit) for income taxes:
Net income	(55,854)	(52,453)	(112,682)	(118,351)
Comprehensive income	$ (55,854)	$ (52,453)	$ (112,682)	$ (118,351)