Business, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Impact of Adopting CECL (Consolidated Statements of Operations) (Details) - USD ($) $ / shares in Units, $ in Thousands							3 Months Ended							9 Months Ended
	Jul. 20, 2023	Jul. 19, 2023	Apr. 19, 2023	Jan. 18, 2023	Apr. 13, 2022	Jan. 19, 2022	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Total interest income							$ 139,383				$ 89,137			$ 403,010	$ 225,402
Total interest expense							60,806				19,240			158,223	40,915
Net interest income							78,577				69,897			244,787	184,487
Provision for (reversal of) credit losses							8,000				7,314			48,777	(2,912)
Net interest income after provision for (reversal of) credit losses							70,577				62,583			196,010	187,399
Total noninterest income							21,921				15,956			67,883	42,912
Total noninterest expense							64,420				56,113			201,653	179,172
Income before income tax expense							28,078				22,426			62,240	51,139
Income tax expense							(6,337)				(4,936)			(13,511)	(10,994)
Net income before attribution of noncontrolling interest							21,741				17,490			48,729	40,145
Noncontrolling interest							(378)	$ (262)	$ (244)		(44)	$ (72)	$ (1,076)	(884)	(1,192)
Net income attributable to Amerant Bancorp Inc.							$ 22,119	$ 7,308	$ 20,186		$ 17,534	$ 8,424	$ 15,379	$ 49,613	$ 41,337
Basic earnings per common share (in dollars per share)							$ 0.66				$ 0.52			$ 1.48	$ 1.22
Diluted earnings per common share (in dollars per share)							$ 0.66				$ 0.52			$ 1.47	$ 1.21
Dividend Per Share (in dollars per share)	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09
Provision for credit losses										$ 20,900
Cumulative Effect, Period of Adoption, Adjusted Balance
Provision for credit losses										$ 11,100
As Reported
Total interest income											$ 89,137				$ 225,402
Total interest expense											19,240				40,915
Net interest income											69,897				184,487
Provision for (reversal of) credit losses											3,000				(7,000)
Net interest income after provision for (reversal of) credit losses											66,897				191,487
Total noninterest income											15,956				42,912
Total noninterest expense											56,113				179,172
Income before income tax expense											26,740				55,227
Income tax expense											(5,864)				(11,875)
Net income before attribution of noncontrolling interest											20,876				43,352
Noncontrolling interest											(44)				(1,192)
Net income attributable to Amerant Bancorp Inc.											$ 20,920				$ 44,544
Basic earnings per common share (in dollars per share)											$ 0.62				$ 1.31
Diluted earnings per common share (in dollars per share)											0.62				1.30
Dividend Per Share (in dollars per share)											$ 0.09				$ 0.27
As Recast
Total interest income											$ 89,137				$ 225,402
Total interest expense											19,240				40,915
Net interest income											69,897				184,487
Provision for (reversal of) credit losses											7,314				(2,912)
Net interest income after provision for (reversal of) credit losses											62,583				187,399
Total noninterest income											15,956				42,912
Total noninterest expense											56,113				179,172
Income before income tax expense											22,426				51,139
Income tax expense											(4,936)				(10,994)
Net income before attribution of noncontrolling interest											17,490				40,145
Noncontrolling interest											(44)				(1,192)
Net income attributable to Amerant Bancorp Inc.											$ 17,534				$ 41,337
Basic earnings per common share (in dollars per share)											$ 0.52				$ 1.22
Diluted earnings per common share (in dollars per share)											0.52				1.21
Dividend Per Share (in dollars per share)											$ 0.09				$ 0.27
Changes
Total interest income											$ 0				$ 0
Total interest expense											0				0
Net interest income											0				0
Provision for (reversal of) credit losses											4,314				4,088
Net interest income after provision for (reversal of) credit losses											(4,314)				(4,088)
Total noninterest income											0				0
Total noninterest expense											0				0
Income before income tax expense											(4,314)				(4,088)
Income tax expense											928				881
Net income before attribution of noncontrolling interest											(3,386)				(3,207)
Noncontrolling interest											0				0
Net income attributable to Amerant Bancorp Inc.											$ (3,386)				$ (3,207)
Basic earnings per common share (in dollars per share)											$ (0.10)				$ (0.09)
Diluted earnings per common share (in dollars per share)											(0.10)				(0.09)
Dividend Per Share (in dollars per share)											$ 0				$ 0