Condensed Unconsolidated Holding Companies’ Financial Statements - Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net income (loss) attributable to Amerant Bancorp Inc.	$ 112,921	$ (1,722)	$ 51,334
Stock-based compensation expense	4,782	2,307	6,365
Net cash provided by operating activities	67,431	57,247	78,392
Cash flows from investing activities
Purchases of available for sale securities	(425,864)	(399,202)	(445,892)
Maturities of available for sale securities	446,436	781,983	497,709
Net cash provided by investing activities	385,319	286,339	205,843
Cash flows from financing activities
Proceeds from common stock issued - Class A	0	0	29,218
Proceeds from issuance of Senior Notes, net of issuance costs	0	58,412	0
Redemption of junior subordinated debentures	0	(28,068)	(25,864)
Net cash used in financing activities	(392,928)	(250,524)	(248,621)
Net increase in cash and cash equivalents	59,822	93,062	35,614
Cash and cash equivalents
Beginning of period	214,386	121,324	85,710
End of period	274,208	214,386	121,324
Class A
Cash flows from financing activities
Dividend paid	(2,200)
Mercantil Bank Holding Corporation | Parent Company | Reportable Legal Entities
Cash flows from operating activities
Net income (loss) attributable to Amerant Bancorp Inc.	112,921	(1,723)	51,334
Adjustments to reconcile net (loss) income to net cash used in operating activities - Equity in earnings of subsidiaries	(120,253)	(2,520)	(56,755)
Stock-based compensation expense	927	375	422
Net change in other assets and liabilities	(6,917)	57	(1,339)
Net cash provided by operating activities	(13,322)	(3,811)	(6,338)
Cash flows from investing activities
Dividends received from subsidiary	40,000	0	61,500
Net cash provided by investing activities	40,000	0	61,500
Cash flows from financing activities
Proceeds from common stock issued - Class A	0	0	29,218
Proceeds from issuance of Senior Notes, net of issuance costs	0	58,412	0
Net cash used in financing activities	(45,845)	(10,966)	753
Net increase in cash and cash equivalents	(19,167)	(14,777)	55,915
Cash and cash equivalents
Beginning of period	43,029	57,806	1,891
End of period	23,862	43,029	57,806
Mercantil Bank Holding Corporation | Parent Company | Reportable Legal Entities | Common Stock | Class A
Cash flows from financing activities
Payments for Repurchase of Equity	(36,332)	0	0
Mercantil Bank Holding Corporation | Parent Company | Reportable Legal Entities | Common Stock | Class B
Cash flows from financing activities
Payments for Repurchase of Equity	(9,563)	(69,378)	(28,465)
Mercantil Florida Bancorp, Inc | Subsidiaries | Reportable Legal Entities
Cash flows from operating activities
Net income (loss) attributable to Amerant Bancorp Inc.	120,254	2,520	56,755
Adjustments to reconcile net (loss) income to net cash used in operating activities - Equity in earnings of subsidiaries	(122,311)	(1,433)	(60,555)
Net change in other assets and liabilities	1,838	(3,823)	3,108
Net cash provided by operating activities	(219)	(2,736)	(692)
Cash flows from investing activities
Dividends received from subsidiary	30,000	0	105,000
Dividends paid	0	0
Purchases of available for sale securities	0	(3,505)	(998)
Maturities of available for sale securities	0	2,000	0
Net cash provided by investing activities	30,000	(1,505)	104,002
Cash flows from financing activities
Redemption of junior subordinated debentures	0	(28,068)	(25,864)
Dividend paid	(40,000)	0	61,500
Net cash used in financing activities	(40,000)	(28,068)	(87,364)
Net increase in cash and cash equivalents	(10,219)	(32,309)	15,946
Cash and cash equivalents
Beginning of period	16,559	48,868	32,922
End of period	$ 6,340	$ 16,559	$ 48,868