v3.26.1
Document And Entity Information - USD ($)
$ in Thousands
 12 Months Ended
Jun. 30, 2026
Sep. 08, 2026
Dec. 31, 2025
Document Information Line Items      
Entity Central Index Key 0001070524    
Document Type 10-K    
Document Annual Report true    
Current Fiscal Year End Date --06-30    
Document Period End Date Jun. 30, 2026    
Document Fiscal Year Focus 2026    
Document Transition Report false    
Entity File Number 0-25165    
Entity Registrant Name GREENE COUNTY BANCORP, INC.    
Entity Incorporation, State or Country Code X1    
Entity Tax Identification Number 14-1809721    
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    
City Area Code 518    
Local Phone Number 943-2600    
Title of 12(b) Security Common Stock, $0.10 par value    
Trading Symbol GCBC    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 147,069
Entity Common Stock, Shares Outstanding   17,025,485  
Auditor Name Bonadio LLP    
Auditor Location Pittsford, New York    
Auditor Firm ID 1884    
Amendment Flag false    
Document Fiscal Period Focus FY