| Cover Page Cover Page | Oct. 21, 2021 | Jul. 22, 2021 | Sep. 30, 2021 |
| Document Information [Line Items] | |||
| Document Period End Date | Oct. 21, 2021 | ||
| Document Type | 8-K | ||
| Document Period End Date | Oct. 21, 2021 | ||
| Entity Registrant Name | HERITAGE FINANCIAL CORP | ||
| Entity File Number | 000-29480 | ||
| Entity Incorporation, State or Country Code | WA | ||
| Entity Tax Identification Number | 91-1857900 | ||
| Entity Address, Address Line One | 201 Fifth Avenue SW, | ||
| Entity Address, City or Town | Olympia | ||
| Entity Address, State or Province | WA | ||
| Entity Address, Postal Zip Code | 98501 | ||
| City Area Code | (360) | ||
| Local Phone Number | 943-1500 | ||
| Written Communications | false | ||
| Soliciting Material | false | ||
| Pre-commencement Tender Offer | false | ||
| Pre-commencement Issuer Tender Offer | false | ||
| Title of 12(b) Security | Common stock, no par value | ||
| Trading Symbol | HFWA | ||
| Security Exchange Name | NASDAQ | ||
| Entity Emerging Growth Company | false | ||
| Entity Central Index Key | 0001046025 | ||
| Amendment Flag | false |
