Document and Entity Information - USD ($)	12 Months Ended
	Jun. 30, 2015	Sep. 11, 2015	Dec. 31, 2014
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 Public Float			$ 43,967,000
Entity Common Stock, Shares Outstanding		4,224,457
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Document Type	10-K/A
Amendment Flag	true
Amendment Description	Greene County Bancorp, Inc. (the “Company”) is filing this Amendment No. 1 (the “Amendment No. 1”) to its Annual Report on Form 10-K for the fiscal year ended June 30, 2015, which was originally filed on September 28, 2015 (the “Original Filing”) for the sole purpose of furnishing Exhibit 101 to the Form 10-K in accordance with Rule 405 of Regulation S-T. Exhibit 101 to Amendment No. 1 provides the consolidated financial statements and related notes from the Form 10-K formatted in XBRL (eXtensible Business Reporting Language). Other than the addition of Exhibit 101, no other changes have been made to the Original Filing.
Document Period End Date	Jun. 30, 2015