Statements of Cash Flows (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows from Operating Activities:
Net income (loss)	$ (3,971,981)us-gaap_NetIncomeLoss	$ 4,089,602us-gaap_NetIncomeLoss	$ (4,829,192)us-gaap_NetIncomeLoss
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
(Increase) decrease in commodity futures trading account - cash and cash equivalents	(4,576,085)	3,466,968	5,715,124
Unrealized (gain) loss on futures contracts	6,009,940	(1,996,630)	(7,676,740)
(Increase) decrease in receivable from General Partner	34,314	(32,077)	44,666
(Increase) decrease in dividends receivable	425	(249)	(228)
(Increase) decrease in interest receivable	0	0	8
(Increase) decrease in directors' fees and insurance receivable	(277)	(688)	526
(Increase) decrease in ETF transaction fees receivable	(350)	0	0
Increase (decrease) in investment payable	0	0	(8)
Increase (decrease) in General Partner management fees payable	(7,276)	(10,280)	13,964
Increase (decrease) in professional fees payable	(70,453)	25,229	(25,802)
Increase (decrease) in brokerage commissions payable	(1,027)	(1,400)	(252)
Increase (decrease) in license fees payable	(372)	(790)	714
Net cash provided by (used in) operating activities	(2,583,142)	5,539,685	(6,757,220)
Cash Flows from Financing Activities:
Addition of partnership shares	4,169,264	5,962,931	33,083,248
Redemption of partnership shares	(11,987,259)unl_PaymentsToPartnershipRedemption	(25,655,241)unl_PaymentsToPartnershipRedemption	(6,377,911)unl_PaymentsToPartnershipRedemption
Net cash provided by (used in) financing activities	(7,817,995)	(19,692,310)	26,705,337
Net Increase (Decrease) in Cash and Cash Equivalents	(10,401,137)	(14,152,625)	19,948,117
Cash and Cash Equivalents, beginning of year	25,514,584	39,667,209	19,719,092
Cash and Cash Equivalents, end of year	$ 15,113,447	$ 25,514,584	$ 39,667,209

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