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Cover - shares
 3 Months Ended
Dec. 31, 2024
Feb. 03, 2025
Document and Entity Information    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Dec. 31, 2024  
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 Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding (in shares)   7,955,453
Entity Registrant Name TIMBERLAND BANCORP, INC.  
Entity Central Index Key 0001046050  
Current Fiscal Year End Date --09-30  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q1  
Amendment Flag false