v3.10.0.1
Document and Entity Information - shares
9 Months Ended
Jun. 30, 2018
Jul. 31, 2018
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2018  
Document Fiscal Year Focus 2018  
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   53,392,840