v3.25.2
Cover - USD ($)
$ in Thousands
 12 Months Ended
Jun. 30, 2025
Sep. 04, 2025
Dec. 31, 2024
Document Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Transition Report false    
Document Financial Statement Error Correction [Flag] false    
Entity Interactive Data Current Yes    
ICFR Auditor Attestation Flag true    
Amendment Flag false    
Document Period End Date Jun. 30, 2025    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Entity Information [Line Items]      
Entity Registrant Name GREENE COUNTY BANCORP, INC.    
Entity Central Index Key 0001070524    
Entity File Number 0-25165    
Entity Tax Identification Number 14-1809721    
Entity Incorporation, State or Country Code X1    
Current Fiscal Year End Date --06-30    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Shell Company false    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
Entity Public Float     $ 177,217
Entity Contact Personnel [Line Items]      
Entity Address, Address Line One 302 Main Street    
Entity Address, City or Town Catskill    
Entity Address, State or Province NY    
Entity Address, Postal Zip Code 12414    
Entity Phone Fax Numbers [Line Items]      
City Area Code 518    
Local Phone Number 943-2600    
Entity Listings [Line Items]      
Title of 12(b) Security Common Stock, $0.10 par value    
Trading Symbol GCBC    
Security Exchange Name NASDAQ    
Entity Common Stock, Shares Outstanding   17,026,828