Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue:
Oil and natural gas									$ 688,743	$ 422,529	$ 348,207
Other									4,295	1,104	120
Total Revenues	142,610	183,992	184,087	182,349	138,899	86,668	99,270	98,796	693,038	423,633	348,327
Costs and expenses:
Lease operating									165,841	94,850	70,281
Transportation									3,568	615	779
Exploration expenditures and dry hole costs									26,555	18,799	14,268
Impairments									2,937	8,883	32,466
Depreciation, depletion and amortization									200,359	113,581	104,624
Accretion of liability for asset retirement obligations									28,299	15,565	15,942
General and administrative									28,137	23,208	18,741
Taxes, other than on earnings									11,490	13,007	14,365
Gain on sale of assets									(28,681)
Other									34,942	4,678	9,735
Total costs and expenses	122,077	143,178	98,535	109,657	86,235	67,379	68,071	71,501	473,447	293,186	281,201
Income from operations	20,533	40,814	85,552	72,692	52,664	19,289	31,199	27,295	219,591	130,447	67,126
Other income (expense):
Interest income									99	136	102
Interest expense									(52,368)	(28,568)	(17,548)
Loss on derivative instruments									(32,361)	(13,305)	(5,870)
Loss on early extinguishment of debt											(2,377)
Total other income (expense)									(84,630)	(41,737)	(25,693)
Income before income taxes									134,961	88,710	41,433
Deferred income tax expense									(49,687)	(29,900)	(14,822)
Net income	$ (12,058)	$ (1,284)	$ 69,579	$ 29,037	$ 24,153	$ (2,247)	$ 35,401	$ 1,503	$ 85,274	$ 58,810	$ 26,611
Basic earnings per share	$ (0.31)	$ (0.03)	$ 1.77	$ 0.74	$ 0.62	$ (0.06)	$ 0.90	$ 0.04	$ 2.18	$ 1.50	$ 0.66
Diluted earnings per share	$ (0.31)	$ (0.03)	$ 1.75	$ 0.73	$ 0.61	$ (0.06)	$ 0.90	$ 0.04	$ 2.15	$ 1.50	$ 0.66
Weighted average common shares used in computing earnings per share:
Basic									38,730	38,885	39,946
Diluted									39,236	39,034	40,050