XML 17 R1.htm IDEA: XBRL DOCUMENT v3.5.0.2
Document And Entity Information - shares
 9 Months Ended
Sep. 30, 2016
Nov. 02, 2016
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2016  
Document Fiscal Year Focus 2016  
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 Filer Category Accelerated Filer  
Trading Symbol USL  
Entity Common Stock, Shares Outstanding   6,450,000