XML 16 R1.htm IDEA: XBRL DOCUMENT v3.25.1
Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2024
Mar. 13, 2025
Jun. 30, 2024
Document Information [Line Items]      
Entity Central Index Key 0001530249    
Entity Registrant Name FS Bancorp, Inc.    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2024    
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
Document Transition Report false    
Entity File Number 001-35589    
Entity Incorporation, State or Country Code WA    
Entity Tax Identification Number 45-4585178    
Entity Address, Address Line One 6920 220th Street SW    
Entity Address, City or Town Mountlake Terrace    
Entity Address, State or Province WA    
Entity Address, Postal Zip Code 98043    
City Area Code 425    
Local Phone Number 771-5299    
Title of 12(b) Security Common Stock, $0.01 par value per share    
Trading Symbol FSBW    
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     $ 255,164,361
Entity Common Stock, Shares Outstanding   7,762,827  
Auditor Name Moss Adams LLP    
Auditor Location Everett, Washington    
Auditor Firm ID 659