Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:
Oil, natural gas and natural gas liquids revenues	$ 80,324	$ 67,747	$ 233,325	$ 207,341
Transportation and marketing-related revenues	1,090	954	3,393	2,643
Total revenues	81,414	68,701	236,718	209,984
Operating costs and expenses:
Lease operating expenses	26,185	24,821	78,496	78,271
Cost of purchased natural gas	792	662	2,486	1,808
Dry hole and exploration costs	1,150	1,809	2,469	5,664
Production taxes	2,911	2,587	8,751	8,394
Asset retirement obligations accretion expense	1,185	1,335	3,744	3,763
Depreciation, depletion and amortization	27,936	28,141	86,439	81,127
General and administrative expenses	8,928	10,296	30,671	32,562
Impairment of oil and natural gas properties	143	853	8,141	17,752
Total operating costs and expenses	69,230	70,504	221,197	229,341
Operating income (loss)	12,184	(1,803)	15,521	(19,357)
Other (expense) income, net:
Realized gains on derivatives, net	4,878	29,835	20,098	88,628
Unrealized losses on derivatives, net	(16,525)	(65,870)	(24,512)	(38,672)
Interest expense	(12,858)	(12,808)	(37,291)	(36,487)
Other (expense) income, net	(10)	408	232	382
Total other (expense) income, net	(24,515)	(48,435)	(41,473)	13,851
Loss before income taxes and equity in (losses) income of unconsolidated affiliates	(12,331)	(50,238)	(25,952)	(5,506)
Income taxes	67	193	(326)	(904)
Loss before equity in (losses) income of unconsolidated affiliates	(12,264)	(50,045)	(26,278)	(6,410)
Equity in (losses) income of unconsolidated affiliates	(50)	26	237	(60)
Net loss	$ (12,314)	$ (50,019)	$ (26,041)	$ (6,470)
Net loss per limited partner unit:
Basic	$ (0.29)	$ (1.15)	$ (0.63)	$ (0.15)
Diluted	$ (0.29)	$ (1.15)	$ (0.63)	$ (0.15)
Weighted average limited partner units outstanding:
Basic	42,599	42,452	42,578	41,784
Diluted	42,599	42,452	42,578	41,784
Distributions declared per unit	$ 0.770	$ 0.766	$ 2.307	$ 2.295