Condensed Consolidating Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating revenue:
Oil production	$ 186,925	$ 201,758
Gas production	36,822	28,857
Natural gas liquids production	9,178	13,452
Other operational income	807	890
Total operating revenue	233,732	244,957
Operating expenses:
Lease operating expenses	53,044	44,480
Transportation, processing and gathering expenses	5,397	3,657
Production taxes	2,089	3,378
Depreciation, depletion, amortization	75,435	84,575
Accretion expense	8,263	8,266
Salaries, general and administrative	13,952	13,705
Incentive compensation expense	1,431	1,442
Derivative expense, net	1,221	485
Other operational expenses	72	42
Total operating expenses	160,904	160,030
Income (loss) from operations	72,828	84,927
Other (income) expenses:
Interest expense	9,635	5,731
Interest income	(117)	(31)
Other income	(726)	(420)
(Income) loss from investment in subsidiaries
Total other (income) expenses	8,792	5,280
Income (loss) before taxes	64,036	79,647
Provision (benefit) for income taxes:
Current	(3,746)	1,234
Deferred	27,024	27,439
Total income taxes	23,278	28,673
Net income	40,758	50,974
Comprehensive income	22,417	28,909
Parent
Operating revenue:
Oil production	5,343	6,234
Gas production	7,198	5,631
Natural gas liquids production	2,299	3,864
Other operational income	649	694
Total operating revenue	15,489	16,423
Operating expenses:
Lease operating expenses	2,291	4,904
Transportation, processing and gathering expenses	2,052	2,488
Production taxes	867	1,163
Depreciation, depletion, amortization	10,191	11,477
Accretion expense	93	148
Salaries, general and administrative	13,948	12,654
Incentive compensation expense	1,431	1,442
Other operational expenses	50	42
Total operating expenses	30,923	34,318
Income (loss) from operations	(15,434)	(17,895)
Other (income) expenses:
Interest expense	9,627	5,846
Interest income	(80)	(30)
Other income	(224)	(19)
(Income) loss from investment in subsidiaries	(56,828)	(66,137)
Total other (income) expenses	(47,505)	(60,340)
Income (loss) before taxes	32,071	42,445
Provision (benefit) for income taxes:
Current	(3,746)	1,234
Deferred	(4,941)	(9,763)
Total income taxes	(8,687)	(8,529)
Net income	40,758	50,974
Comprehensive income	22,417	28,909
Guarantor Subsidiary
Operating revenue:
Oil production	181,582	195,524
Gas production	29,624	23,226
Natural gas liquids production	6,879	9,588
Other operational income	158	63
Total operating revenue	218,243	228,401
Operating expenses:
Lease operating expenses	50,753	39,387
Transportation, processing and gathering expenses	3,345	1,169
Production taxes	1,222	2,215
Depreciation, depletion, amortization	65,244	73,000
Accretion expense	8,170	8,032
Salaries, general and administrative	4	1,051
Incentive compensation expense
Derivative expense, net	1,221	485
Other operational expenses	22
Total operating expenses	129,981	125,339
Income (loss) from operations	88,262	103,062
Other (income) expenses:
Interest expense	8	(115)
Interest income	(37)	(1)
Other income	(502)	(401)
(Income) loss from investment in subsidiaries		239
Total other (income) expenses	(531)	(278)
Income (loss) before taxes	88,793	103,340
Provision (benefit) for income taxes:
Current
Deferred	31,965	37,202
Total income taxes	31,965	37,202
Net income	56,828	66,138
Comprehensive income	56,828	66,138
Non-Guarantor Subsidiaries
Operating revenue:
Gas production
Natural gas liquids production
Other operational income		133
Total operating revenue		133
Operating expenses:
Lease operating expenses		189
Transportation, processing and gathering expenses
Production taxes
Depreciation, depletion, amortization		98
Accretion expense		86
Salaries, general and administrative
Incentive compensation expense
Derivative expense, net
Other operational expenses
Total operating expenses		373
Income (loss) from operations		(240)
Other (income) expenses:
Income (loss) before taxes		(240)
Provision (benefit) for income taxes:
Current
Deferred
Total income taxes
Net income		(240)
Comprehensive income		(240)
Eliminations
Operating expenses:
Depreciation, depletion, amortization
Accretion expense
Other (income) expenses:
(Income) loss from investment in subsidiaries	56,828	65,898
Total other (income) expenses	56,828	65,898
Income (loss) before taxes	(56,828)	(65,898)
Provision (benefit) for income taxes:
Current
Deferred
Total income taxes
Net income	(56,828)	(65,898)
Comprehensive income	$ (56,828)	$ (65,898)