| Document and Entity Information | Apr. 21, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Apr. 21, 2021 |
| Entity Registrant Name | FIRST BANCORP, INC |
| Entity Central Index Key | 0000765207 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | ME |
| Entity File Number | 0-26589 |
| Entity Tax Identification Number | 01-0404322 |
| Entity Address, Address Line One | Main Street |
| Entity Address, City or Town | Damariscotta |
| Entity Address, State or Province | ME |
| Entity Address, Postal Zip Code | 04543 |
| City Area Code | 207 |
| Local Phone Number | 563-3195 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
