Document and Entity Information
| Document and Entity Information | Apr. 22, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 22, 2021 |
| Entity Registrant Name | Meridian Bancorp, Inc. |
| Entity Incorporation, State or Country Code | MD |
| Entity File Number | 001-36573 |
| Entity Tax Identification Number | 00-0000000 |
| Entity Address, Address Line One | 10 MERIDIAN STREET |
| Entity Address, City or Town | EAST BOSTON |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02128 |
| City Area Code | 617 |
| Local Phone Number | 567-1500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001600125 |
| Title of 12(b) Security | Common stock, $0.01 par value per share |
| Trading Symbol | EBSB |
| Security Exchange Name | NASDAQ |