Document and Entity Information - shares	6 Months Ended
	Dec. 31, 2016	Feb. 13, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	GREENE COUNTY BANCORP INC
Entity Central Index Key	0001070524
Current Fiscal Year End Date	--06-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		8,502,614
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2016