Cover - $ / shares		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jul. 31, 2020
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date		Jun. 30, 2020
Document Transition Report	false
Entity File Number	000-23333
Entity Incorporation, State or Country Code	WA
Entity Tax Identification Number	91-1863696
Entity Address, Address Line One	624 Simpson Avenue
Entity Address, City or Town	Hoquiam
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98550
City Area Code	(360)
Local Phone Number	533-4747
Title of 12(b) Security	Common stock, $.01 par value
Trading Symbol	TSBK
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)			8,310,793
Common stock par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Entity Registrant Name		TIMBERLAND BANCORP INC,
Entity Central Index Key		0001046050
Current Fiscal Year End Date		--09-30
Document Fiscal Year Focus		2020
Document Fiscal Period Focus		Q3
Amendment Flag		false