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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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