| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | S-1/A |
| Interest income | | | | | | | | |
| Loans | 293.2 | 216.1 | 220.9 | 263.0 | 257.6 | 223.8 | 188.5 | |
| Investment securities | 41.4 | 31.5 | 39.0 | 47.2 | 49.2 | 47.9 | 49.5 | |
| Interest earning deposits with banks | 4.2 | 0.2 | 0.6 | 2.8 | 2.5 | 1.6 | 0.8 | |
| Total interest income | 338.8 | 247.8 | 260.6 | 313.0 | 309.4 | 273.3 | 238.8 | 208.2 |
| |
| Interest expense | | | | | | | | |
| Interest bearing demand deposits | 15.1 | 0.6 | 0.4 | 0.9 | 0.7 | 0.4 | 0.7 | 1.2 |
| Savings and money market deposits | 11.8 | 3.5 | 7.1 | 15.7 | 12.9 | 8.9 | 8.3 | 7.4 |
| Time deposits | 22.1 | 23.8 | 45.8 | 51.8 | 42.2 | 26.8 | 16.6 | 8.0 |
| Advances from the Federal Home Loan Bank | 15.1 | 8.6 | 13.2 | 24.3 | 26.5 | 18.2 | 11.0 | |
| |
| Senior notes | | | | | | | | |
| Subordinated notes | 1.2 | | | 7.2 | 8.1 | 7.5 | 7.1 | |
| Junior subordinated debentures | 1.2 | | | 7.2 | 8.1 | 7.5 | 7.1 | |
| Securities sold under agreements to repurchase | 0.0 | 0.0 | 0.0 | | | | | |
| Total interest expense | 72.1 | 42.7 | 71.0 | 99.9 | 90.3 | 63.6 | 46.9 | 35.9 |
| Net interest income | 266.7 | 205.1 | 189.6 | 213.1 | 219.0 | 209.7 | 191.9 | 172.3 |
| Provision for (reversal of) credit losses | 13.9 | -16.5 | 88.6 | -3.2 | 0.4 | -3.5 | 22.1 | |
| Net interest income after provision for (reversal of) credit losses | 252.7 | 221.6 | 100.9 | 216.2 | 218.7 | 213.2 | 169.8 | |
| |
| Noninterest income | | | | | | | | |
| Deposits and service fees | 18.6 | 17.2 | 15.8 | 17.1 | 17.8 | 19.6 | 20.9 | 21.1 |
| Brokerage, advisory and fiduciary activities | 17.7 | 18.6 | 16.9 | 14.9 | 16.8 | 20.6 | 20.3 | |
| Gain (loss) on early extinguishment of advances from the Federal Home Loan Bank, net | 10.7 | -2.5 | -0.1 | -0.9 | 0.9 | | 0.7 | |
| Loan level derivative income | 10.4 | 4.0 | 3.2 | | | | | |
| Change in cash surrender value of bank owned life insurance | 5.4 | 5.5 | 5.7 | 5.7 | 5.8 | 5.5 | 4.4 | |
| Cards and trade finance servicing fees | 2.3 | 1.8 | 1.3 | 3.9 | 4.4 | 4.6 | 4.3 | 5.2 |
| Derivative gains, net | 0.5 | | | | | | | |
| Gain on sale of headquarters building | | 62.4 | | | | | | |
| Securities (losses) gains, net | -3.7 | 3.7 | 27.0 | | | | | |
| Other noninterest income | 5.5 | 10.0 | 3.6 | 7.7 | 6.6 | 19.3 | 6.2 | |
| Total noninterest income | 67.3 | 120.6 | 73.5 | 57.1 | 53.9 | 71.5 | 62.3 | 54.8 |
| |
| Noninterest expense | | | | | | | | |
| Salaries and employee benefits | 123.5 | 117.6 | 111.5 | 137.4 | 141.8 | 131.8 | 129.7 | |
| Occupancy and equipment | 27.4 | 20.4 | 17.6 | 16.2 | 16.5 | 17.4 | 18.4 | |
| Professional and other services fees | 22.1 | 19.1 | 13.1 | 16.1 | 19.1 | 16.4 | 11.9 | |
| Telecommunication and data processing | 14.7 | 14.9 | 12.9 | 13.1 | 12.4 | 9.8 | 8.4 | |
| Advertising expenses | 11.6 | 3.4 | 1.6 | | | | | |
| Loan level derivative expense | 8.1 | 0.8 | 0.3 | | | | | |
| Contract termination costs | 7.1 | | | | | | | |
| FDIC assessments and insurance | 6.6 | 6.4 | 6.1 | 4.0 | 6.2 | 7.6 | 7.1 | |
| Depreciation and amortization | 5.9 | 7.3 | 9.4 | 7.1 | 8.5 | 9.0 | 9.1 | |
| Other real estate owned valuation expense | 3.4 | | | | | | | |
| Loans held for sale valuation expense | 0.2 | | | | | | | |
| Other operating expenses | 10.7 | 8.4 | 6.1 | 15.4 | 10.4 | 15.6 | 13.7 | |
| Total noninterest expenses | 241.4 | 198.2 | 178.7 | 209.3 | 215.0 | 207.6 | 198.3 | 192.3 |
| Income (loss) before income tax (expense) benefit | 78.6 | 144.0 | -4.3 | 64.0 | | | | |
| Income tax (expense) benefit | -16.6 | -33.7 | 2.6 | -12.7 | -11.7 | -34.0 | -10.2 | -8.5 |
| Net income (loss) before attribution of noncontrolling interest | 62.0 | 110.3 | -1.7 | 51.3 | | | | |
| Noncontrolling interest | 1.3 | 2.6 | | | | | | |
| Net income (loss) attributable to Amerant Bancorp Inc. | 63.3 | 112.9 | -1.7 | 51.3 | 45.8 | 43.1 | 23.6 | |
| |
| Other comprehensive (loss) income, net of tax | | | | | | | | |
| Net unrealized holding (losses) gains on debt securities available for sale arising during the period | -97.2 | -13.0 | 39.9 | | | | | |
| Net unrealized holding gains (losses) on cash flow hedges arising during the period | 0.2 | 0.1 | -1.7 | | | | | |
| Reclassification adjustment for items included in net income | 1.1 | -3.6 | -19.8 | -2.6 | 0.6 | | | |
| Other comprehensive (loss) income | -95.9 | -16.4 | 18.4 | 31.4 | -12.0 | 4.6 | -1.2 | |
| Comprehensive (loss) income | -32.5 | 96.5 | 16.7 | 82.7 | 33.8 | 47.6 | 22.3 | 2.2 |
| |
| Earnings (Loss) Per Share (Note 23) | | | | | | | | |
| Basic earnings (loss) per common share (in dollars per share) | $1.87 | $3.04 | ($0.04) | $1.21 | $1.08 | $1.01 | $0.55 | $0.35 |
| Diluted earnings (loss) per common share (in dollars per share) | $1.85 | $3.01 | ($0.04) | $1.20 | $1.08 | $1.01 | $0.55 | $0.35 |