SUPPLEMENTAL FINANCIAL INFORMATION ON OIL AND NATURAL GAS EXPLORATION, DEVELOPMENT AND PRODUCTION ACTIVITIES (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Oil & Gas properties [Abstract]
Unproved oil and gas properties	$ 7,478	$ 9,169
Proved oil and gas properties	136,521	119,919
Total capitalized costs	143,999	129,088
DD&A per equivalent BOE (in dollars per BOE)	32.06	33.49	31.64
Undeveloped properties [Abstract]
Acquisitions	2,067	271	5,006	134
Exploration	0	0	0	0
Development	0	0	0	0
Undeveloped property costs	2,067	271	5,006	134
Total Acquisitions	7,478
Total Exploration	0
Total Development	0
Total undeveloped property costs	7,478	9,200
Property acquisition costs:
Proved	445	2,987	1,288
Unproved	1,760	1,416	10,679
Exploration costs	9,138	10,943	32,788
Development costs	9,403	20,134	4,550
Total costs incurred	20,746	35,480	49,305
Results of operations from oil and natural gas producing activities [Abstract]
Oil and gas revenues	33,647	32,534	30,958
Operating expenses	10,469	10,788	11,552
Depreciation, depletion and amortization	13,623	14,893	13,997
Impairment	5,828	5,189	0
Total operating expenses	29,920	30,870	25,549
Operating income	3,727	1,664	5,409
Standardized measure of discounted future net cash flows relating to USE's ownership interests in proved oil and natural gas reserves [Abstract]
Future cash inflows	330,245	237,148	259,533
Future costs:
Production	(129,392)	(96,616)	(77,813)
Development	(37,739)	(21,461)	(42,972)
Future income tax expense	(14,500)	(8,483)	(19,790)
Future net cash flows	148,614	110,588	118,958
10% discount factor	(43,761)	(39,571)	(56,767)
Standardized measure of discounted future net cash flows	104,853	71,017	62,191
Period for calculating unescalated average prices prior to the end of reporting period	12 months
Discount factor (in hundredths)	10.00%
Changes in standardized measure of future net cash flows relating to proved oil and natural gas reserves [Roll Forward]
Balance at beginning of year	71,017	62,191	44,653
Sales of oil and gas, net of production costs	(23,179)	(21,747)	(19,406)
Net change in prices and production costs	2,543	(4,548)	1,401
Net change in future development costs	0	0	0
Extensions and discoveries	54,360	23,297	26,574
Purchase of reserves in place	0	2,573	3,082
Sale of reserves in place	0	(13,573)	(1,947)
Revisions of previous quantity estimates	(2,961)	(5,927)	(3,158)
Development costs incurred during year	8,344	22,808	14,930
Previously estimated development costs incurred	(6,414)	(9,706)	(2,719)
Net change in income taxes	(4,245)	7,261	(4,270)
Accretion of discount	7,647	7,254	5,207
Changes in production rates, timing and other	(2,259)	1,134	(2,156)
Balance at end of year	$ 104,853	$ 71,017	$ 62,191	$ 44,653
Oil (BBLS) [Member]
Proved Developed and Undeveloped Reserves [Roll forward]
Beginning of year	2,613,643	2,737,969
Revisions of previous quantity estimates	(162,957)	(145,596)
Extensions, discoveries and improved recoveries	1,352,746	763,125
Purchase of reserves in place	0	75,948
Sales of reserves in place	0	(444,272)
Production	(343,719)	(373,531)
End of year	3,459,713	2,613,643	2,737,969
Proved developed reserves at end of year	1,875,528	1,770,659
Pricing used in cash flow estimates (in BBLS or MCFE)	96.78	94.71	96.19
Natural Gas or NGL (MCFE) [Member]
Proved Developed and Undeveloped Reserves [Roll forward]
Beginning of year	1,798,088	2,744,128
Revisions of previous quantity estimates	382,690	(481,583)
Extensions, discoveries and improved recoveries	678,412	369,169
Purchase of reserves in place	0	30,457
Sales of reserves in place	0	(437,057)
Production	(487,282)	(427,026)
End of year	2,371,908	1,798,088	2,744,128
Proved developed reserves at end of year	1,701,282	1,420,295
Pricing used in cash flow estimates (in BBLS or MCFE)	3.67	2.757	4.12