Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2021	Nov. 30, 2021	Mar. 31, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	SGU
Title of 12(b) Security	Common Units
Security Exchange Name	NYSE
Entity Registrant Name	STAR GROUP, L.P.
Entity Central Index Key	0001002590
Entity Tax Identification Number	06-1437793
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity File Number	001-14129
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		38,610,861
Entity Public Float			$ 374,735,728
Entity Address, Address Line One	9 West Broad Street
Entity Address, Address Line Two	Suite 310
Entity Address, City or Town	Stamford
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06902
City Area Code	(203)
Local Phone Number	328-7310
ICFR Auditor Attestation Flag	true