XML 53 R1.htm IDEA: XBRL DOCUMENT v3.20.1
Document and Entity Information - shares
 3 Months Ended
Mar. 31, 2020
May 12, 2020
Document and Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2020  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q1  
Entity Registrant Name United States 12 Month Natural Gas Fund, LP  
Entity Central Index Key 0001405513  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Trading Symbol UNL  
Entity Common Stock, Shares Outstanding   450,000
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false