Note 10 - Fair Values of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($)		Sep. 30, 2023	Dec. 31, 2022
Securities available for sale		$ 592,305,000	$ 602,936,000
Loan, Mortgage, Held-for-Sale, Fair Value Disclosure		10,200,000	3,600,000
Fair Value, Inputs, Level 1 [Member]
Securities available for sale		0	0
Reported Value Measurement [Member]
Securities available for sale	[1]	592,305,000	602,936,000
FHLBI stock	[2]	21,513,000	17,721,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents		265,987,000	96,772,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Loans, net		4,056,368,000	3,874,373,000
Mortgage servicing rights		11,391,000	11,837,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Loan, Mortgage, Held-for-Sale, Fair Value Disclosure		10,171,000	3,565,000
Accrued interest receivable		19,607,000	15,476,000
Deposits		3,900,735,000	3,712,811,000
Repurchase agreements		164,082,000	194,340,000
FHLBI advances		457,910,000	308,263,000
Accrued interest payable		7,218,000	3,223,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Subordinated Debentures [Member]
Subordinated debt		49,473,000	48,958,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Subordinated Notes [Member]
Subordinated debt		88,885,000	88,628,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Interest rate swaps		35,060,000	25,697,000
Interest rate swaps		35,242,000	25,900,000
Estimate of Fair Value Measurement [Member]
Securities available for sale	[1]	592,305,000	602,936,000
FHLBI stock	[2]	21,513,000	17,721,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents		265,987,000	96,772,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Loans, net		3,953,468,000	3,800,042,000
Mortgage servicing rights		19,451,000	17,727,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Loan, Mortgage, Held-for-Sale, Fair Value Disclosure		10,246,000	3,643,000
Accrued interest receivable		19,607,000	15,476,000
Deposits		3,558,860,000	3,379,403,000
Repurchase agreements		164,082,000	194,340,000
FHLBI advances		434,992,000	292,044,000
Accrued interest payable		7,218,000	3,223,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Subordinated Debentures [Member]
Subordinated debt		56,009,000	49,531,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Subordinated Notes [Member]
Subordinated debt		77,528,000	75,024,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member]
Interest rate swaps		35,060,000	25,697,000
Interest rate swaps		$ 35,242,000	$ 25,900,000

[1] See Note 11 for a description of the fair value hierarchy as well as a disclosure of levels for classes of financial assets and liabilities.

[2] It is not practical to determine the fair value of FHLBI stock due to transferability restrictions; therefore, fair value is estimated at carrying amount.