| Cover | Jan. 19, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 19, 2021 |
| Entity File Number | 001-38676 |
| Entity Registrant Name | Bank First Corporation |
| Entity Central Index Key | 0001746109 |
| Entity Tax Identification Number | 39-1435359 |
| Entity Incorporation, State or Country Code | WI |
| Entity Address, Address Line One | 402 North 8th Street |
| Entity Address, City or Town | Manitowoc |
| Entity Address, State or Province | WI |
| Entity Address, Postal Zip Code | 54220 |
| City Area Code | 920 |
| Local Phone Number | 652-3100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | BFC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
