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Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2016	Aug. 09, 2016
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q2
Entity Registrant Name	United States 12 Month Natural Gas Fund, LP
Entity Central Index Key	0001405513
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Trading Symbol	UNL
Entity Common Stock, Shares Outstanding		1,400,000

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