| Cover Page | Jul. 29, 2021 | Apr. 13, 2021 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Oct. 28, 2021 | |
| Entity Registrant Name | Amalgamated Financial Corp. | |
| Entity Incorporation, State or Country Code | DE | |
| Entity File Number | 001-40136 | |
| Entity Tax Identification Number | 85-2757101 | |
| Entity Address, Address Line One | 275 Seventh Avenue | |
| Entity Address, City or Town | New York | |
| Entity Address, State or Province | NY | |
| Entity Address, Postal Zip Code | 10001 | |
| City Area Code | 212 | |
| Local Phone Number | 895-8988 | |
| 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 | AMAL | |
| Security Exchange Name | NASDAQ | |
| Entity Emerging Growth Company | true | |
| Entity Ex Transition Period | false | |
| Entity Central Index Key | 0001823608 | |
| Amendment Flag | false |
