Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 06, 2023
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	Q3
Document Fiscal Year Focus	2023
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
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 Emerging Growth Company	false
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		9,618,440