Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 18,907	$ 7,486
Accounts receivable:
Oil, natural gas and natural gas liquids revenues	35,967	34,909
Related party	4,138	1,422
Other	4,047	11,263
Derivative asset, net	14,132	40,771
Other current assets	1,777	1,750
Total current assets	78,968	97,601
Oil and natural gas properties, net of accumulated depreciation, depletion and amortization; March 31, 2013, $420,005; December 31, 2012, $389,206	1,863,584	1,875,890
Other property, net of accumulated depreciation and amortization; Marchr 31, 2013, $636; December 31, 2012, $598	1,317	1,325
Long-term derivative asset, net	36,268	45,839
Investments in uncosolidated affilates	103,018	34,545
Other assets	9,631	10,214
Total assets	2,092,786	2,065,414
Accounts payable and accrued liabilities:
Accounts payable and accrued liabilities	53,852	40,171
Derivative liability	1,554
Total current liabilities	55,406	40,171
Asset retirement obligations	104,103	102,707
Long-term debt	944,237	859,218
Long-term derivative liability	1,189
Other long-term liabilities	1,444	3,494
Owners' equity:
Common unitholders - 42,599,080 units and 42,320,707 units issued and outstanding as of March 31, 2013 and December 31, 2012, respectively	999,937	1,072,175
General partner interest	(13,530)	(12,351)
Total owners' equity	986,407	1,059,824
Total liabilities and owners' equity	$ 2,092,786	$ 2,065,414