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					6 Months Ended
	Apr. 19, 2023	Jan. 18, 2023	Apr. 13, 2022	Jan. 19, 2022	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Total interest income					$ 138,497			$ 71,167		$ 263,627	$ 136,265
Total interest expense					54,620			12,222		97,417	21,675
Net interest income					83,877			58,945		166,210	114,590
Reversal of credit losses					29,077			(951)		40,777	(10,226)
Net interest income after provision for (reversal of) credit losses					54,800			59,896		125,433	124,816
Total noninterest income					26,619			12,931		45,962	26,956
Total noninterest expense					72,500			62,241		137,233	123,059
Income before income tax expense					8,919			10,586		34,162	28,713
Income tax expense					(1,873)			(2,234)		(7,174)	(6,058)
Net income before attribution of noncontrolling interest					7,046			8,352		26,988	22,655
Noncontrolling interest					(262)	$ (244)		(72)	$ (1,076)	(506)	(1,148)
Net income attributable to Amerant Bancorp Inc.					$ 7,308	$ 20,186		$ 8,424	$ 15,379	$ 27,494	$ 23,803
Basic earnings per common share (in dollars per share)					$ 0.22			$ 0.25		$ 0.82	$ 0.70
Diluted earnings per common share (in dollars per share)					$ 0.22			$ 0.25		$ 0.81	$ 0.69
Cash dividends declared per common share (in dollars per share)	$ 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								$ 71,167			$ 136,265
Total interest expense								12,222			21,675
Net interest income								58,945			114,590
Reversal of credit losses								0			(10,000)
Net interest income after provision for (reversal of) credit losses								58,945			124,590
Total noninterest income								12,931			26,956
Total noninterest expense								62,241			123,059
Income before income tax expense								9,635			28,487
Income tax expense								(2,033)			(6,011)
Net income before attribution of noncontrolling interest								7,602			22,476
Noncontrolling interest								(72)			(1,148)
Net income attributable to Amerant Bancorp Inc.								$ 7,674			$ 23,624
Basic earnings per common share (in dollars per share)								$ 0.23			$ 0.69
Diluted earnings per common share (in dollars per share)								0.23			0.68
Cash dividends declared per common share (in dollars per share)								$ 0.09			$ 0.18
As Recast
Total interest income								$ 71,167			$ 136,265
Total interest expense								12,222			21,675
Net interest income								58,945			114,590
Reversal of credit losses								(951)			(10,226)
Net interest income after provision for (reversal of) credit losses								59,896			124,816
Total noninterest income								12,931			26,956
Total noninterest expense								62,241			123,059
Income before income tax expense								10,586			28,713
Income tax expense								(2,234)			(6,058)
Net income before attribution of noncontrolling interest								8,352			22,655
Noncontrolling interest								(72)			(1,148)
Net income attributable to Amerant Bancorp Inc.								$ 8,424			$ 23,803
Basic earnings per common share (in dollars per share)								$ 0.25			$ 0.70
Diluted earnings per common share (in dollars per share)								0.25			0.69
Cash dividends declared per common share (in dollars per share)								$ 0.09			$ 0.18
Changes
Total interest income								$ 0			$ 0
Total interest expense								0			0
Net interest income								0			0
Reversal of credit losses								(951)			(226)
Net interest income after provision for (reversal of) credit losses								951			226
Total noninterest income								0			0
Total noninterest expense								0			0
Income before income tax expense								951			226
Income tax expense								(201)			(47)
Net income before attribution of noncontrolling interest								750			179
Noncontrolling interest								0			0
Net income attributable to Amerant Bancorp Inc.								$ 750			$ 179
Basic earnings per common share (in dollars per share)								$ 0.02			$ 0.01
Diluted earnings per common share (in dollars per share)								0.02			0.01
Cash dividends declared per common share (in dollars per share)								$ 0			$ 0