UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 836	$ 599
Accounts receivable	45,290	60,239
Short-term derivative instruments	259,854	272,320
Prepaid expenses and other current assets	4,839	7,028
Total current assets	310,819	340,186
Property and equipment, at cost:
Oil and natural gas properties, successful efforts method	3,639,835	3,616,325
Support equipment and facilities	206,147	205,876
Other	2,491	2,671
Accumulated depreciation, depletion and impairment	(1,931,091)	(1,878,549)
Property and equipment, net	1,917,382	1,946,323
Long-term derivative instruments	442,616	461,810
Restricted investments	154,766	152,631
Other long-term assets	4,519	5,053
Total assets	2,830,102	2,906,003
Current liabilities:
Accounts payable	6,863	8,792
Accounts payable - affiliates	5,137	3,339
Revenues payable	25,427	25,504
Accrued liabilities (Note 2)	61,744	52,923
Short-term derivative instruments	2,098	2,850
Total current liabilities	101,269	93,408
Long-term debt (Note 7)	1,957,984	2,000,579
Asset retirement obligations	164,964	162,989
Long-term derivative instruments	2,161	1,441
Deferred tax liabilities	2,158	2,094
Total liabilities	$ 2,228,536	$ 2,260,511
Commitments and contingencies (Note 12)
Partners' equity:
General partner (86,797 units outstanding at March 31, 2016 and December 31, 2015)	$ 799	$ 848
Total partners' equity	601,566	645,492
Total liabilities and equity	2,830,102	2,906,003
Limited Partners Common Units [Member]
Partners' equity:
Limited partners units	$ 600,767	$ 644,644