Securities - Schedule of Available for Sale Securities with Unrealized Losses (Details) $ in Thousands	Sep. 30, 2025 USD ($) contract	Dec. 31, 2024 USD ($) contract
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Number of Securities \| contract	15	148
Less Than 12 Months, Estimated Fair Value	$ 73,667	$ 781,183
Less Than 12 Months, Unrealized Loss	$ (301)	$ (14,817)
12 Months or More, Number of Securities \| contract	392	405
12 Months or Longer, Estimated Fair Value	$ 584,217	$ 501,806
12 Months or More, Unrealized Loss	(26,660)	(40,917)
Total, Estimated Fair Value	657,884	1,282,989
Total, Unrealized Loss	$ (26,961)	$ (55,734)
U.S. Government agency and sponsored enterprise residential MBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Number of Securities \| contract	10	133
Less Than 12 Months, Estimated Fair Value	$ 56,483	$ 717,487
Less Than 12 Months, Unrealized Loss	$ (249)	$ (13,555)
12 Months or More, Number of Securities \| contract	315	324
12 Months or Longer, Estimated Fair Value	$ 490,929	$ 407,841
12 Months or More, Unrealized Loss	(23,325)	(34,982)
Total, Estimated Fair Value	547,412	1,125,328
Total, Unrealized Loss	$ (23,574)	$ (48,537)
Non-agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Number of Securities \| contract	0	0
Less Than 12 Months, Estimated Fair Value	$ 0	$ 0
Less Than 12 Months, Unrealized Loss	$ 0	$ 0
12 Months or More, Number of Securities \| contract	1	1
12 Months or Longer, Estimated Fair Value	$ 7,144	$ 11,792
12 Months or More, Unrealized Loss	(176)	(725)
Total, Estimated Fair Value	7,144	11,792
Total, Unrealized Loss	$ (176)	$ (725)
U.S. Government agency and sponsored enterprise commercial MBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Number of Securities \| contract	2	13
Less Than 12 Months, Estimated Fair Value	$ 16,971	$ 63,468
Less Than 12 Months, Unrealized Loss	$ (51)	$ (1,261)
12 Months or More, Number of Securities \| contract	31	30
12 Months or Longer, Estimated Fair Value	$ 72,463	$ 64,606
12 Months or More, Unrealized Loss	(2,746)	(4,676)
Total, Estimated Fair Value	89,434	128,074
Total, Unrealized Loss	$ (2,797)	$ (5,937)
U.S. Government agency and sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Number of Securities \| contract	3	2
Less Than 12 Months, Estimated Fair Value	$ 213	$ 228
Less Than 12 Months, Unrealized Loss	$ (1)	$ (1)
12 Months or More, Number of Securities \| contract	42	47
12 Months or Longer, Estimated Fair Value	$ 12,071	$ 15,982
12 Months or More, Unrealized Loss	(291)	(387)
Total, Estimated Fair Value	12,284	16,210
Total, Unrealized Loss	$ (292)	$ (388)
Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Number of Securities \| contract	0	0
Less Than 12 Months, Estimated Fair Value	$ 0	$ 0
Less Than 12 Months, Unrealized Loss	$ 0	$ 0
12 Months or More, Number of Securities \| contract	3	3
12 Months or Longer, Estimated Fair Value	$ 1,610	$ 1,585
12 Months or More, Unrealized Loss	(122)	(147)
Total, Estimated Fair Value	1,610	1,585
Total, Unrealized Loss	$ (122)	$ (147)

Amerant Bancorp Inc. 10-Q