v3.26.1
Document And Entity Information - shares
 6 Months Ended
Jun. 30, 2026
Jul. 31, 2026
Document Information [Line Items]    
Entity Central Index Key 0001693577  
Entity Registrant Name MainStreet Bancshares, Inc.  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q2  
Document Fiscal Year Focus 2026  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Transition Report false  
Entity File Number 001-38817  
Entity Incorporation, State or Country Code VA  
Entity Tax Identification Number 81-2871064  
Entity Address, Address Line One 10089 Fairfax Boulevard  
Entity Address, City or Town Fairfax  
Entity Address, State or Province VA  
Entity Address, Postal Zip Code 22030  
City Area Code 703  
Local Phone Number 481-4567  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   7,121,076
Depositary Shares [Member]    
Document Information [Line Items]    
Title of 12(b) Security Depositary Shares  
Trading Symbol MNSBP  
Security Exchange Name NASDAQ  
Common Stock [Member]    
Document Information [Line Items]    
Title of 12(b) Security Common Stock  
Trading Symbol MNSB  
Security Exchange Name NASDAQ