| Document and Entity Information | Jan. 21, 2021 |
| Document and Entity Information | |
| Document Type | 8-K |
| Document Period End Date | Jan. 21, 2021 |
| Entity Registrant Name | 1st Source Corp |
| Entity Incorporation, State or Country Code | IN |
| Entity File Number | 0-6233 |
| Entity Tax Identification Number | 35-1068133 |
| Entity Address, Address Line One | 100 North Michigan Street |
| Entity Address, City or Town | South Bend |
| Entity Address, State or Province | IN |
| Entity Address, Postal Zip Code | 46601 |
| City Area Code | 574 |
| Local Phone Number | 235-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock - without par value |
| Trading Symbol | SRCE |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0000034782 |
