Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Nature of Operations - Washington Federal, Inc. (the "Company") is a Washington corporation headquartered in Seattle, Washington. The Company is a bank holding company that conducts its operations through its national bank subsidiary, Washington Federal Bank, National Association (the "Bank"). The Bank is principally engaged in the business of attracting deposits from businesses and the general public and investing these funds, together with borrowings and other funds, in commercial and consumer loans. As used throughout this document, the terms "Washington Federal" or the "Company" refer to Washington Federal, Inc. and its consolidated subsidiaries and the term "Bank" refers to the operating subsidiary Washington Federal Bank, National Association. Basis of Presentation - The Company has prepared the consolidated unaudited interim financial statements included in this report. All intercompany transactions and accounts have been eliminated in consolidation. The preparation of financial statements, in conformity with accounting principles generally accepted in the United States of America (“GAAP”), requires management to make estimates and assumptions that affect amounts reported in the financial statements. Actual results could differ from these estimates. In the opinion of management, all adjustments (consisting only of normal recurring adjustments) necessary for a fair presentation are reflected in the interim financial statements. Certain amounts in the financial statements from prior periods have been reclassified to conform to the current financial statement presentation. The information included in this Form 10-Q should be read in conjunction with the financial statements and related notes in the Company's 2018 Annual Report on Form 10-K (“2018 Annual Financial Statements”). Interim results are not necessarily indicative of results for a full year. Summary of Significant Accounting Policies - The significant accounting policies used in preparation of the Company's consolidated financial statements are disclosed in its 2018 Annual Financial Statements. There have not been any material changes in the Company's significant accounting policies compared to those contained in its 2018 Annual Financial Statements for the year ended September 30, 2018. Restricted Cash Balances - Based on the level of vault cash on hand, the Company was not required to maintain cash reserve balances with the Federal Reserve Bank as of June 30, 2019. As of June 30, 2019 and September 30, 2018, the Company pledged cash collateral related to derivative contracts of $23,050,000 and $18,000,000, respectively. Equity Securities - The Company records equity securities within Other assets in its Consolidated Statements of Financial Condition. Investments in equity securities with readily determinable fair values (marketable) are measured at fair value, with changes in the fair value recognized as a component of Other income in the Consolidated Statements of Operations. Investments in equity investments that do not have readily determinable fair values (non-marketable) are accounted for at cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer, also referred to as the measurement alternative. Any adjustments to the carrying value of these investments are recorded in Other income in the Consolidated Statements of Operations. Off-Balance-Sheet Credit Exposures - The only material off-balance-sheet credit exposures are loans in process and unused lines of credit, which had a combined balance of $2,252,249,000 and $2,180,162,000 at June 30, 2019 and September 30, 2018, respectively. The Company estimates losses on off-balance-sheet credit exposures by allocating a loss percentage derived from historical loss factors for each asset class.