Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Cash	$ 25,144	$ 17,433
Accounts receivable	35,302	32,263
Due from affiliates	9,319	3,734
Derivative instruments	42,482	32,683
Prepaid and other current assets	659	249
Total current assets	112,906	86,362
Noncurrent assets:
Evaluated	1,270,689	975,182
Unevaluated	9,000
Gross oil and natural gas properties	1,279,689	975,182
Gas processing equipment	4,110	865
Less accumulated depreciation, depletion and amortization	(141,912)	(80,484)
Total property and equipment, net	1,141,887	895,563
Derivative instruments	81,450	70,570
Deferred taxes		270
Other assets	11,408	4,279
Total noncurrent assets	1,234,745	970,682
Total assets	1,347,651	1,057,044
Current liabilities:
Current portion of asset retirement obligations	845	348
Derivative instruments	5,176	9,569
Accrued and other liabilities	60,182	50,027
Total current liabilities	66,203	59,944
Noncurrent liabilities:
Long-term debt	620,946	500,000
Derivative instruments	14,156	16,906
Asset retirement obligations	73,507	65,353
Other liabilities	6,755
Deferred taxes	102
Total noncurrent liabilities	715,466	582,259
Commitments and contingencies (see Note 11)
Partners' capital:
Class C convertible preferred unitholders (16,666,667 issued and outstanding as of September 30, 2012 and December 31, 2011)	369,278	358,138
General partner (41,747 and 35,729 units issued and outstanding as of September 30, 2012 and December 31, 2011)	614	546
Total partners' capital	565,982	414,841
Total liabilities and partners' capital	1,347,651	1,057,044
Limited Partners-Public Common [Member]
Partners' capital:
Limited partners' capital account	258,578	241,306
Limited Partners-Affiliated - Common [Member]
Partners' capital:
Limited partners' capital account		(113,414)
Limited Partners-Affiliated - Subordinated [Member]
Partners' capital:
Limited partners' capital account	$ (62,488)	$ (71,735)