| Document and Entity Information | Apr. 29, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | MID PENN BANCORP INC |
| Amendment Flag | false |
| Entity Central Index Key | 0000879635 |
| Document Type | 8-K |
| Document Period End Date | Apr. 29, 2021 |
| Entity Incorporation State Country Code | PA |
| Entity File Number | 1-13677 |
| Entity Tax Identification Number | 25-1666413 |
| Entity Address, Address Line One | 349 Union Street |
| Entity Address, City or Town | Millersburg |
| Entity Address, State or Province | PA |
| City Area Code | 1.866 |
| Local Phone Number | 642.7736 |
| Entity Address, Postal Zip Code | 17061 |
| Security 12b Title | Common Stock, $1.00 par value per share |
| Trading Symbol | MPB |
| Security Exchange Name | NASDAQ |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
