XML 30 R1.htm IDEA: XBRL DOCUMENT v2.4.0.6
Document and Entity Information (USD $)
 12 Months Ended
Dec. 31, 2011
Mar. 26, 2012
Jun. 30, 2011
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2011    
Document Fiscal Year Focus 2011    
Document Fiscal Period Focus FY    
Trading Symbol UNL    
Entity Registrant Name UNITED STATES 12 MONTH NATURAL GAS FUND, LP    
Entity Central Index Key 0001405513    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Common Stock, Shares Outstanding   1,650,000  
Entity Public Float     $ 35,926,000