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CONTRACTS AND AGREEMENTS (Brokerage Commissions) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Total commissions accrued to brokers	$ 372	$ 318
Total commissions as annualized percentage of average total net assets	0.03%	0.02%
Rebalancing Investments Transaction [Member]
Total commissions accrued to brokers	$ 274	$ 185
Total commissions as annualized percentage of average total net assets	73.66%	58.18%
Creation And Redemption Activity [Member]
Total commissions accrued to brokers	$ 98	$ 133
Total commissions as annualized percentage of average total net assets	26.34%	41.82%

X

- Definition

Percentage of Average Daily Net Assets

+ References

No definition available.

+ Details

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Namespace Prefix:	unl_
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X

- Definition

The amount of expense during the period for floor brokerage fees paid to other broker-dealers to execute trades on their behalf, stock exchange fees, order flow fees, and clearance fees.

+ References

No definition available.

+ Details

Name:	us-gaap_FloorBrokerageExchangeAndClearanceFees
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=unl_CreationAndRedemptionActivityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: