EARNINGS PER SHARE - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Net income attributable to Amalgamated Financial Corp.	$ 27,249	$ 21,338
Dividends paid on preferred stock	0	0
Income attributable to common stock	$ 27,249	$ 21,338
Weighted average common shares outstanding, basic (in shares)	30,476	30,706
Basic earnings per common share (in dollars per share)	$ 0.89	$ 0.69
Incremental shares from assumed conversion of options and RSUs (in shares)	261	233
Weighted average common shares outstanding, diluted (in shares)	30,737	30,939
Diluted earnings per common share (in dollars per share)	$ 0.89	$ 0.69