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Customer Accounts - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Banking and Thrift, Interest [Abstract]
Customer accounts over $250,000	$ 7,198,111	$ 5,491,395

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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

Customer Accounts Greater than $250,000

+ References

No definition available.

+ Details

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Namespace Prefix:	wfsl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant