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v3.25.3

REVENUE FROM CONTRACTS WITH CUSTOMERS (Details) | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024
Revenue from Contract with Customer [Abstract] |  |
Revenue streams percentage, contract with customer | 3.60% | 3.20%

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Revenue From Contract With Customer, Percentage + References No definition available. + Details
Name: | wfsl_RevenueFromContractWithCustomerPercentage
Namespace Prefix: | wfsl_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration