v3.10.0.1
Document and Entity Information - USD ($)
12 Months Ended
Sep. 30, 2018
Nov. 30, 2018
Mar. 31, 2018
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Sep. 30, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Trading Symbol SGU    
Entity Registrant Name STAR GROUP, L.P.    
Entity Central Index Key 0001002590    
Current Fiscal Year End Date --09-30    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Common Stock, Shares Outstanding   52,755,392  
Entity Public Float     $ 467,138,000