Document and Entity Information |
12 Months Ended |
|---|---|
Dec. 31, 2024 | |
| Document and Entity Information [Abstract] | |
| Document Type | DEF 14A |
| Entity Registrant Name | JOHN MARSHALL BANCORP, INC. |
| Entity Central Index Key | 0001710482 |
| Amendment Flag | false |
Insider Trading Policies and Procedures |
12 Months Ended |
|---|---|
Dec. 31, 2024 | |
| Insider Trading Policies and Procedures [Line Items] | |
| Insider Trading Policies and Procedures Adopted | true |