v3.26.1
Document and Entity Information - shares
 6 Months Ended
Jun. 30, 2026
Aug. 14, 2026
Document and Entity Information    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Fiscal Year Focus 2026  
Document Transition Report false  
Entity File Number 333-291808  
Entity Registrant Name Ballston Spa Bancorp, Inc.  
Entity Incorporation, State or Country Code NY  
Entity Tax Identification Number 74-2245601  
Entity Address, Address Line One 990 State Route 67  
Entity Address, City or Town Ballston Spa  
Entity Address State Or Province NY  
Entity Address, Postal Zip Code 12020  
City Area Code 518  
Local Phone Number 363-8199  
Title of 12(b) Security Common Stock, par value $12.50 per share  
Trading Symbol BSPA  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   1,100,071
Entity Central Index Key 0002094107  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q2  
Amendment Flag false