Condensed Statements of Operations (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Gain (loss) on trading of commodity futures contracts:
Realized gain (loss) on closed positions	$ (2,280,826)us-gaap_GainLossOnSaleOfInvestments	$ 1,641,740us-gaap_GainLossOnSaleOfInvestments
Change in unrealized gain (loss) on open positions	975,025us-gaap_UnrealizedGainLossOnInvestments	508,810us-gaap_UnrealizedGainLossOnInvestments
Dividend income	716us-gaap_DividendIncomeOperating	550us-gaap_DividendIncomeOperating
Interest income	635us-gaap_InterestIncomeOperating	713us-gaap_InterestIncomeOperating
ETF transaction fees	2,100us-gaap_FeesAndCommissions	3,150us-gaap_FeesAndCommissions
Total income (loss)	(1,302,350)us-gaap_Revenues	2,154,963us-gaap_Revenues
Expenses
General Partner management fees (Note 3)	32,443us-gaap_AssetManagementCosts	44,676us-gaap_AssetManagementCosts
Professional fees	21,266us-gaap_ProfessionalFees	46,980us-gaap_ProfessionalFees
Brokerage commissions	1,595	2,070
Directors' and insurance fees	1,032us-gaap_NoninterestExpenseDirectorsFees	1,780us-gaap_NoninterestExpenseDirectorsFees
License fees	649us-gaap_LicenseCosts	894us-gaap_LicenseCosts
Total expenses	56,985us-gaap_OperatingExpenses	96,400us-gaap_OperatingExpenses
Expense waiver (Note 3)	(17,835)unl_ExpenseWaiver	(38,045)unl_ExpenseWaiver
Net expenses	39,150unl_NetOperatingExpenses	58,355unl_NetOperatingExpenses
Net income (loss)	$ (1,341,500)us-gaap_NetIncomeLoss	$ 2,096,608us-gaap_NetIncomeLoss
Net income (loss) per limited partnership share	$ (1.09)	$ 1.31
Net income (loss) per weighted average limited partnership share	$ (1.02)	$ 1.69
Weighted average limited partnership shares outstanding	1,317,778	1,238,333

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