Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 01, 2020
Document Information [Abstract]
Entity Registrant Name	First Northwest Bancorp
Entity Central Index Key	0001556727
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2020
Entity Current Reporting Status	Yes
Entity Small Business	true
Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Common Stock, Shares Outstanding		10,428,963