| Cover | Jan. 21, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 21, 2021 |
| Entity File Number | 001-38282 |
| Entity Registrant Name | METROPOLITAN BANK HOLDING CORP. |
| Entity Central Index Key | 0001476034 |
| Entity Tax Identification Number | 13-4042724 |
| Entity Incorporation, State or Country Code | NY |
| Entity Address, Address Line One | 99 Park Avenue |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10016 |
| City Area Code | 212 |
| Local Phone Number | 659-0600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | MCB |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
