| Document and Entity Information | Oct. 21, 2020 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 21, 2020 |
| Entity Registrant Name | HarborOne Bancorp, Inc. |
| Entity Incorporation, State or Country Code | MA |
| Entity File Number | 001-38955 |
| Entity Tax Identification Number | 81-1607465 |
| Entity Address, Address Line One | 770 Oak Street |
| Entity Address, City or Town | Brockton |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02301 |
| City Area Code | 508 |
| Local Phone Number | 895-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value |
| Trading Symbol | HONE |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001769617 |
| Amendment Flag | false |
