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Basis of Presentation and Summary of Significant Accounting Policies (Details Textual) $ in Thousands | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2025 USD ($) segment subsidiary reporting_unit | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2006
Significant Accounting Policies [Line Items] |  |  |  |  |
Date of incorporation | Sep. 15, 2005 |  |  |  |
Number of wholly owned subsidiaries | subsidiary | 3 |  |  |  |
Number of reporting units | reporting_unit | 1 |  |  |  |
Number of reportable segments | segment | 1 |  |  |  |
Decrease to retained earnings | $ (193,320) | $ (230,622) |  |  |
Allowance for credit losses - loans | 55,686 | 44,769 | $ 38,774 | $ 31,737 |
Allowance related to off-balance sheet credit exposures | 2,585 | 2,139 | $ 3,745 | 0 |
Allowance for credit loss on HTM securities | $ 101 | $ 154 |  |  |
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Decrease to retained earnings |  |  |  | 4,500 |
Allowance for credit losses - loans |  |  |  | 2,962 |
Allowance related to off-balance sheet credit exposures |  |  |  | 2,504 |
Cumulative Effect, Period of Adoption, Adjustment, Net Of Tax |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Allowance for credit losses - loans |  |  |  | 2,300 |
Allowance related to off-balance sheet credit exposures |  |  |  | 1,900 |
Allowance for credit loss on HTM securities |  |  |  | $ 300 |
First Internet Bank of Indiana |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Ownership (as a percent) |  |  |  |  | 100.00%
Equipment | Minimum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives (in years) | 3 years |  |  |  |
Equipment | Maximum |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives (in years) | 5 years |  |  |  |
Land improvements |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives (in years) | 10 years |  |  |  |
Buildings |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Estimated useful lives (in years) | 39 years |  |  |  |

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