| Cover Page Cover Page | May 29, 2020 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | May 29, 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 |
