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Summary of Significant Accounting Policies - Additional Information (Detail)				6 Months Ended
	Jun. 30, 2012	Feb. 29, 2012 Redemption Baskets	Feb. 29, 2012 Prior to February 29, 2012 Redemption Baskets	Jun. 30, 2012 Maximum
Significant Accounting Policies [Line Items]
Basis points subtracted from overnight Federal Funds Rate	0.32%
Minimum likelihood of tax benefits being recognized upon ultimate settlement	50.00%
Number of units per basket		50,000	100,000
Cash equivalents maturity period				6 months

X

- Definition

Cash Equivalents, Maturity Period

+ References

No definition available.

+ Details

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Namespace Prefix:	unl_
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Period Type:	duration

X

- Definition

Market yields, basis point

+ References

No definition available.

+ Details

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Namespace Prefix:	unl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of Units per Basket

+ References

No definition available.

+ Details

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Namespace Prefix:	unl_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage Of Income Tax Examination Minimum Likelihood of Tax Benefits Being Realized Upon Settlement

+ References

No definition available.

+ Details

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Namespace Prefix:	unl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

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Namespace Prefix:	unl_
Data Type:	xbrli:stringItemType
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