| Document and Entity Information | Oct. 15, 2019 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 14, 2020 |
| Entity Registrant Name | WASHINGTON FEDERAL INC |
| Entity Central Index Key | 0000936528 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | WA |
| Entity File Number | 001-34654 |
| Entity Tax Identification Number | 91-1661606 |
| Entity Address, Address Line One | 425 Pike Street |
| Entity Address, City or Town | Seattle |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98101 |
| City Area Code | 206 |
| Local Phone Number | 624-7930 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
