| Document and Entity Information | Nov. 20, 2020 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | Amerant Bancorp Inc. |
| Amendment Flag | false |
| Entity Central Index Key | 0001734342 |
| Document Type | 8-K |
| Document Period End Date | Nov. 20, 2020 |
| Entity Incorporation State Country Code | FL |
| Entity File Number | 001-38534 |
| Entity Tax Identification Number | 65-0032379 |
| Entity Address, Address Line One | 220 Alhambra Circle |
| Entity Address, City or Town | Coral Gables |
| Entity Address, State or Province | FL |
| Entity Address, Postal Zip Code | 33134 |
| City Area Code | (305) |
| Local Phone Number | 460-8728 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Class A Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Class A Common Stock |
| Trading Symbol | AMTB |
| Security Exchange Name | NASDAQ |
| Class B Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Class B Common Stock |
| Trading Symbol | AMTBB |
| Security Exchange Name | NASDAQ |
