Note 16 - Fair Values of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($)		Dec. 31, 2020	Dec. 31, 2019
Securities available for sale		$ 387,347,000	$ 334,655,000
Servicing Asset at Fair Value, Amount, Ending Balance		10,000,000.0	7,400,000
Reported Value Measurement [Member]
Securities available for sale	[1]	387,347,000	334,655,000
Federal Home Loan Bank stock	[2]	18,002,000	18,002,000
Securities sold under agreements to repurchase		118,365,000	102,675,000
Federal Home Loan Bank advances		394,000,000	354,000,000
Estimate of Fair Value Measurement [Member]
Securities available for sale	[1]	387,347,000	334,655,000
Federal Home Loan Bank stock	[2]	18,002,000	18,002,000
Securities sold under agreements to repurchase		118,365,000	102,675,000
Federal Home Loan Bank advances		410,881,000	361,887,000
Fair Value, Inputs, Level 1 [Member]
Securities available for sale		0	0
Fair Value, Inputs, Level 1 [Member] | Reported Value Measurement [Member]
Cash		16,953,000	16,430,000
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Cash		16,953,000	16,430,000
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]
Cash equivalents		609,053,000	217,301,000
Loans held for sale		22,888,000	4,978,000
Servicing Asset at Fair Value, Amount, Ending Balance		8,189,000	4,652,000
Accrued interest receivable		10,861,000	9,944,000
Deposits		3,411,553,000	2,690,384,000
Subordinated debentures		47,563,000	46,881,000
Accrued interest payable		2,313,000	3,949,000
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Cash equivalents		609,053,000	217,301,000
Loans held for sale		24,029,000	4,978,000
Servicing Asset at Fair Value, Amount, Ending Balance		10,006,000	7,375,000
Accrued interest receivable		10,861,000	9,944,000
Deposits		3,397,768,000	2,600,452,000
Subordinated debentures		47,574,000	46,140,000
Accrued interest payable		2,313,000	3,949,000
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Loans, net		3,155,503,000	2,827,800,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Loans, net		$ 3,294,522,000	$ 2,887,168,000

[1] See Note 17 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.