Document and Entity Information - shares
9 Months Ended
Jun. 30, 2019
Jul. 30, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Trading Symbol SGU  
Entity Registrant Name STAR GROUP, L.P.  
Entity Central Index Key 0001002590  
Current Fiscal Year End Date --09-30  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   49,280,628
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Current Reporting Status Yes  
Entity File Number 001-14129  
Entity Tax Identification Number 061437793  
Entity Address, Address Line One 9 West Broad Street  
Entity Address, City or Town Stamford  
Entity Address, State or Province Connecticut  
Entity Address, Postal Zip Code 06902  
City Area Code (203)  
Local Phone Number 328-7310