Supplemental Condensed Consolidating Financial Information (Supplemental Condensed Consolidating Statement of Operations) (Details) (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
Oil and natural gas									$ 422,529	$ 348,207	$ 239,770
Other									1,104	120	139
Total Revenue	138,899	86,668	99,270	98,796	103,364	84,884	92,830	67,249	423,633	348,327	239,909
Lease operating									94,850	70,281	52,365
Transportation									615	779	1,306
Exploration expenditures and dry hole costs									18,799	14,268	6,441
Impairments									8,883	32,466	26,142
Depreciation, depletion and amortization									113,581	104,624	104,561
Accretion of liability for asset retirement obligations									15,565	15,942	12,845
General and administrative									23,208	18,741	18,078
Taxes, other than on earnings									13,007	14,365	10,133
Other									4,678	9,735	729
Total costs and expenses	86,235	67,379	68,071	71,501	90,223	69,232	61,571	60,175	293,186	281,201	232,600
Income from operations	52,664	19,289	31,199	27,295	13,141	15,652	31,259	7,074	130,447	67,126	7,309
Interest income									136	102	113
Interest expense									(28,568)	(17,548)	(9,807)
Gain (loss) on derivative instruments									(13,305)	(5,870)	(4,865)
Loss on early extinguishment of debt								2,400		(2,377)	(5,627)
Total other income (expense)									(41,737)	(25,693)	(20,186)
Income (loss) before provision for income taxes									88,710	41,433	(12,877)
Deferred income tax benefit (expense)									(29,900)	(14,822)	4,409
Total provision for income taxes									(29,900)	(14,822)	4,409
Net income (loss)	24,153	(2,247)	35,401	1,503	(7,341)	23,458	25,003	(14,509)	58,810	26,611	(8,468)
Parent Company [Member]
Oil and natural gas									318,749	245,567	171,176
Other									15,152	15,007	15,008
Total Revenue									333,901	260,574	186,184
Lease operating									71,002	51,618	34,004
Transportation									611	766	1,306
Exploration expenditures and dry hole costs									18,790	14,045	3,237
Impairments									8,883	32,532	25,478
Depreciation, depletion and amortization									92,689	82,168	83,672
Accretion of liability for asset retirement obligations									10,551	9,013	6,018
General and administrative									22,845	18,281	17,737
Taxes, other than on earnings									1,162	(733)	681
Other									5,496	9,940	897
Total costs and expenses									232,029	217,630	173,030
Income from operations									101,872	42,944	13,154
Interest income									136	102	113
Interest expense									(28,568)	(17,548)	(9,807)
Gain (loss) on derivative instruments									(13,305)	(5,870)	(4,865)
Loss on early extinguishment of debt										(2,377)	(5,627)
Income (loss) from equity investments									18,945	15,532	(3,846)
Total other income (expense)									(22,792)	(10,161)	(24,032)
Income (loss) before provision for income taxes									79,080	32,783	(10,878)
Deferred income tax benefit (expense)									(20,270)	(6,172)	2,410
Total provision for income taxes									(20,270)	(6,172)	2,410
Net income (loss)									58,810	26,611	(8,468)
Guarantor Subsidiaries [Member]
Oil and natural gas									103,780	102,640	68,594
Other									952	113	131
Total Revenue									104,732	102,753	68,725
Lease operating									23,848	18,663	18,361
Transportation									4	13
Exploration expenditures and dry hole costs									9	223	3,204
Impairments										(66)	664
Depreciation, depletion and amortization									20,892	22,456	20,889
Accretion of liability for asset retirement obligations									5,014	6,929	6,827
General and administrative									15,363	15,460	15,341
Taxes, other than on earnings									11,845	15,098	9,452
Other									(818)	(205)	(168)
Total costs and expenses									76,157	78,571	74,570
Income from operations									28,575	24,182	(5,845)
Income (loss) before provision for income taxes									28,575	24,182	(5,845)
Deferred income tax benefit (expense)									(9,630)	(8,650)	1,999
Total provision for income taxes									(9,630)	(8,650)	1,999
Net income (loss)									18,945	15,532	(3,846)
Consolidation, Eliminations [Member]
Other									(15,000)	(15,000)	(15,000)
Total Revenue									(15,000)	(15,000)	(15,000)
General and administrative									(15,000)	(15,000)	(15,000)
Total costs and expenses									(15,000)	(15,000)	(15,000)
Income (loss) from equity investments									(18,945)	(15,532)	3,846
Total other income (expense)									(18,945)	(15,532)	3,846
Income (loss) before provision for income taxes									(18,945)	(15,532)	3,846
Net income (loss)									$ (18,945)	$ (15,532)	$ 3,846