| Cover Page Cover Page | Dec. 21, 2020 | Dec. 17, 2020 |
| Document Information [Line Items] | ||
| Document Period End Date | Dec. 17, 2020 | |
| Document Type | 8-K | |
| Document Period End Date | Dec. 17, 2020 | |
| 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 |
