v3.25.2
Document And Entity Information - shares
 6 Months Ended
Jun. 30, 2025
Jul. 31, 2025
Document Information [Line Items]    
Entity Central Index Key 0001556727  
Entity Registrant Name First Northwest Bancorp  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q2  
Document Fiscal Year Focus 2025  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2025  
Document Transition Report false  
Entity File Number 001-36741  
Entity Incorporation, State or Country Code WA  
Entity Tax Identification Number 46-1259100  
Entity Address, Address Line One 105 West 8th Street  
Entity Address, City or Town Port Angeles  
Entity Address, State or Province WA  
Entity Address, Postal Zip Code 98362  
City Area Code 360  
Local Phone Number 457-0461  
Title of 12(b) Security Common Stock, par value $0.01 per share  
Trading Symbol FNWB  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Emerging Growth Company false  
Entity Small Business true  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   9,418,309