| Cover | Feb. 01, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 1, 2021 |
| Entity File Number | 001-38290 |
| Entity Registrant Name | STERLING BANCORP, INC. |
| Entity Central Index Key | 0001680379 |
| Entity Tax Identification Number | 38-3163775 |
| Entity Incorporation, State or Country Code | MI |
| Entity Address, Address Line One | One Towne Square |
| Entity Address, Address Line Two | Suite 1900 |
| Entity Address, City or Town | Southfield |
| Entity Address, State or Province | MI |
| Entity Address, Postal Zip Code | 48076 |
| City Area Code | 248 |
| Local Phone Number | 355-2400 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | SBT |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
