Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Revenues:
Oil, natural gas and natural gas liquids revenues	$ 68,109	$ 39,431	$ 127,730	$ 78,027
Transportation and marketing-related revenues	1,484	1,476	2,885	3,054
Total revenues	69,593	40,907	130,615	81,081
Operating costs and expenses:
Lease operating expenses	17,949	14,869	35,311	26,301
Cost of purchased natural gas	1,120	1,095	2,170	2,315
Dry hole and exploration costs	441		844
Production taxes	3,119	1,673	5,770	3,800
Asset retirement obligations accretion expense	970	764	1,936	1,274
Depreciation, depletion and amortization	18,443	13,436	36,007	25,520
General and administrative expenses	7,132	5,825	15,725	10,549
Impairment of oil and natural gas properties	5,078		6,666
Gain on sale of oil and natural gas properties		(4,388)		(3,824)
Total operating costs and expenses	54,252	33,274	104,429	65,935
Operating income	15,341	7,633	26,186	15,146
Other income (expense), net:
Realized gains on derivatives, net	14,242	13,901	27,784	21,866
Unrealized gains (losses) on derivatives, net	17,422	(2,158)	(35,633)	30,502
Interest expense	(8,124)	(3,269)	(13,283)	(5,372)
Other income, net	313	252	233	393
Total other income (expense), net	23,853	8,726	(20,899)	47,389
Income before income taxes	39,194	16,359	5,287	62,535
Income taxes	(31)	(79)	(113)	(131)
Net income	39,163	16,280	5,174	62,404
General partner's interest in net income, including incentive distribution rights	3,728	2,624	5,982	5,836
Limited partners' interest in net income (loss)	$ 35,435	$ 13,656	$ (808)	$ 56,568
Net income (loss) per limited partner unit:
Basic	1.03	0.50	(0.02)	2.14
Diluted	1.03	0.50	(0.02)	2.14
Weighted average limited partner units outstanding:
Basic	34,294	27,210	33,002	26,403
Diluted	34,534	27,264	33,002	26,438
Distributions declared per unit	$ 0.761	$ 0.757	$ 1.521	$ 1.513