Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, 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
Revenue:
Oil and natural gas									$ 422,529	$ 348,207	$ 239,770
Other									1,104	120	139
Total Revenues	138,899	86,668	99,270	98,796	103,364	84,884	92,830	67,249	423,633	348,327	239,909
Costs and expenses:
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 expense									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
Other income (expense):
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 income taxes									88,710	41,433	(12,877)
Deferred income tax benefit (expense)									(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)
Basic earnings (loss) per share	$ 0.62	$ (0.06)	$ 0.90	$ 0.04	$ (0.19)	$ 0.59	$ 0.62	$ (0.36)	$ 1.50	$ 0.66	$ (0.21)
Diluted earnings (loss) per share	$ 0.61	$ (0.06)	$ 0.90	$ 0.04	$ (0.19)	$ 0.58	$ 0.62	$ (0.36)	$ 1.50	$ 0.66	$ (0.21)
Weighted average common shares used in computing earnings per share:
Basic									38,885	39,946	40,064
Diluted									39,034	40,050	40,064