Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Current assets:
Cash	$ 22,529	$ 17,433
Accounts receivable	36,955	32,263
Due from affiliates	332	3,734
Derivative instruments	61,281	32,683
Prepaid and other current assets	904	249
Total current assets	122,001	86,362
Noncurrent assets:
Evaluated	1,259,868	975,182
Unevaluated	9,000
Gross oil and natural gas properties	1,268,868	975,182
Gas processing equipment	2,552	865
Less accumulated depreciation, depletion and amortization	(120,614)	(80,484)
Total property and equipment, net	1,150,806	895,563
Derivative instruments	115,797	70,570
Deferred taxes		270
Other assets	7,265	4,279
Total noncurrent assets	1,273,868	970,682
Total assets	1,395,869	1,057,044
Current liabilities:
Current portion of asset retirement obligations	808	348
Derivative instruments	9,473	9,569
Accrued and other liabilities	58,162	50,027
Total current liabilities	68,443	59,944
Noncurrent liabilities:
Long-term debt	596,500	500,000
Derivative instruments	20,391	16,906
Asset retirement obligations	71,652	65,353
Other liabilities	6,724
Deferred taxes	320
Total noncurrent liabilities	695,587	582,259
Commitments and contingencies (see Note 11)
Partners' capital:
Class C convertible preferred unitholders (16,666,667 issued and outstanding as of March 31, 2012 and December 31, 2011)	365,527	358,138
General partner (41,747 and 35,729 units issued and outstanding as of June 30, 2012 and December 31, 2011)	672	546
Total partners' capital	631,839	414,841
Total liabilities and partners' capital	1,395,869	1,057,044
Limited Partners-Public Common [Member]
Partners' capital:
Limited partners' capital account	322,932	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	$ (57,292)	$ (71,735)