XML 46 R1.htm IDEA: XBRL DOCUMENT v3.19.3
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 05, 2019
Document and Entity Information    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Entity Registrant Name United States 12 Month Oil Fund, LP  
Entity Central Index Key 0001405528  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Accelerated Filer  
Trading Symbol USL  
Entity Interactive Data Current Yes  
Entity Common Stock, Shares Outstanding   2,550,000
Entity Shell Company false  
Entity Emerging Growth Company false  
Entity Small Business false