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Revenue from Contracts with Customers - Additional Information (Details)	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue streams percentage, contract with customer	4.70%	4.90%

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- References

No definition available.

+ Details

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- Definition

Revenue From Contract With Customer, Percentage

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No definition available.

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Namespace Prefix:	wfsl_
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Balance Type:	na
Period Type:	duration