Condensed Consolidated Statements of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash flows from operating activities:
Net income	$ 5,174	$ 62,404
Adjustments to reconcile net income to net cash flows provided by operating activities:
Asset retirement obligations accretion expense	1,936	1,274
Depreciation, depletion and amortization	36,007	25,520
Equity-based compensation cost	3,877	2,103
Impairment of oil and natural gas properties	6,666
Gain on sale of oil and natural gas properties		(3,824)
Noncash derivative activity	30,951	(30,502)
Amortization of discount on long-term debt	183
Amortization of deferred loan costs	554	275
Other, net	56	(1)
Changes in operating assets and liabilities:
Accounts receivable	(12,866)	(4,098)
Other current assets	111	2,625
Accounts payable and accrued liabilities	7,630	879
Long-term liabilities		(734)
Other, net	(149)	(119)
Net cash flows provided by operating activities	80,130	55,802
Cash flows from investing activities:
Acquisition of oil and natural gas properties	3,101	(147,769)
Development of oil and natural gas properties	(33,686)	(8,170)
Proceeds from sale of oil and natural gas properties	1,170	4,471
Settlements from acquired derivatives	2,834
Earnest money received for sale of oil and natural gas properties	900
Net cash flows used in investing activities	(25,681)	(151,468)
Cash flows from financing activities:
Long-term debt borrowings		138,000
Repayment of long-term debt borrowings	(431,500)	(95,000)
Proceeds from debt offering	292,500
Loan costs incurred	(6,202)	(8)
Proceeds from public equity offering	147,108	92,770
Offering costs	(308)	(154)
Contributions from general partner	3,191	1,977
Distributions paid	(55,973)	(43,433)
Net cash flows (used in) provided by financing activities	(51,184)	94,152
Increase (decrease) in cash and cash equivalents	3,265	(1,514)
Cash and cash equivalents - beginning of period	23,127	18,806
Cash and cash equivalents - end of period	$ 26,392	$ 17,292