Summary Of Significant Accounting Policies (Policies)	3 Months Ended
Summary Of Significant Accounting Policies (Policies)	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation: The accompanying unaudited consolidated financial statements for Timberland Bancorp, Inc. (“Company”) were prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information and with instructions for Form 10-Q and, therefore, do not include all disclosures necessary for a complete presentation of consolidated financial condition, results of operations, and cash flows in conformity with GAAP. However, all adjustments which are, in the opinion of management, necessary for a fair presentation of the interim consolidated financial statements have been included. All such adjustments are of a normal recurring nature. The unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended September 30, 2016 (“2016 Form 10-K”). The unaudited consolidated results of operations for the three months ended December 31, 2016 are not necessarily indicative of the results that may be expected for the entire fiscal year ending September 30, 2017.
Principles of Consolidation	Principles of Consolidation: The unaudited consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, Timberland Bank (“Bank”), and the Bank’s wholly-owned subsidiary, Timberland Service Corporation. All significant intercompany transactions and balances have been eliminated in consolidation.
Operating Segment	Operating Segment: The Company has one reportable operating segment which is defined as community banking in western Washington under the operating name, “Timberland Bank.”
Use of Estimates	The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates.
Reclassification	Certain prior period amounts have been reclassified to conform to the December 31, 2016 presentation with no change to net income or total shareholders’ equity as previously reported.
Recent Accounting Pronouncements	In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606). The core principle of this ASU is that an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In general, the new guidance requires companies to use more judgment and make more estimates than under current guidance, including identifying performance obligations in the contract and estimating the amount of variable consideration to include in the transaction price related to each separate performance obligation. This ASU is effective for annual periods beginning after December 15, 2017, including interim periods within that reporting period. The adoption of ASU No. 2014-09 is not expected to have a material impact on the Company's consolidated financial statements. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. The main provisions of this ASU address the valuation and impairment of certain equity investments along with simplified disclosures about the fair value of financial instruments. The amendments in this ASU are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. The adoption of ASU No. 2016-01 is not expected to have a material impact on the Company's consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This ASU is intended to increase transparency and comparability among organizations by requiring the recognition of lease assets and lease liabilities on the balance sheet and disclosure of key information about leasing arrangements. The principal change required by this ASU relates to lessee accounting, and is that for operating leases, a lessee is required to (1) recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, in the statement of financial position, (2) recognize a single lease cost, calculated so that the cost of the lease is allocated over the lease term on a generally straight-line basis, and (3) classify all cash payments within operating activities in the statement of cash flows. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. If a lessee makes this election, it should recognize lease expense for such leases generally on a straight-line basis over the lease term. This ASU also changes disclosure requirements related to leasing activities and requires certain qualitative disclosures along with specific quantitative disclosures. The amendments in this ASU are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2018. Early application of the amendments in this ASU is permitted. The Company is currently evaluating the impact that the adoption of ASU No. 2016-02 will have on the Company's future consolidated financial statements. In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting. This ASU includes provisions intended to simplify various aspects related to how share-based payments are accounted for and presented in the financial statements. This ASU is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2016. The Company is currently evaluating the impact that the adoption of ASU No. 2016-09 will have on the Company's future consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses. This ASU replaces the existing incurred losses methodology for estimating allowances with a current expected credit losses methodology with respect to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables, loans, held to maturity investment securities and off-balance sheet commitments. In addition, this ASU requires credit losses relating to available for sale debt securities to be recorded through an allowance for credit losses rather than a reduction of the carrying amount. ASU No. 2016-13 also changes the accounting for purchased credit-impaired debt securities and loans. The standard retains many of the current disclosure requirements in current GAAP and expands certain disclosure requirements. This ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The Company is currently evaluating the impact that the adoption of ASU 2016-13 will have on the Company’s future consolidated financial statements. In January 2017, the FASB issued ASU No. 2017-04, Intangibles - Goodwill and Other: Simplifying the Test for Goodwill Impairment. This ASU simplifies the subsequent measurement of goodwill and eliminates Step 2 from the goodwill impairment test. In computing the implied fair value of goodwill under Step 2, an entity had to perform procedures to determine the fair value at the impairment testing date of its assets and liabilities (including unrecognized assets and liabilities) following the procedure that would be required in determining the fair value of assets acquired and liabilities assumed in a business combination. Under ASU No. 2017-04, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. ASU No. 2017-04 will be effective for annual or interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early application of this ASU is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The adoption of ASU No. 2017-04 is not expected to have a material impact on the Company's future consolidated financial statements.