Document and Entity Information	6 Months Ended
	Dec. 31, 2012	Feb. 12, 2013
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2012
Entity Registrant Name	GREENE COUNTY BANCORP INC
Entity Central Index Key	0001070524
Current Fiscal Year End Date	--06-30
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		4,185,671
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2013