Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2019	Jan. 31, 2020
Document and Entity Information
Entity Registrant Name	TIMBERLAND BANCORP INC,
Entity Central Index Key	0001046050
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Small Business	true
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding		8,365,794
Entity Current Reporting Status	Yes