Note 9 - Fair Values of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($)		Sep. 30, 2020	Dec. 31, 2019
Securities available for sale		$ 312,424,000	$ 334,655,000
Reported Value Measurement [Member]
Securities available for sale	[1]	312,424,000	334,655,000
FHLBI stock	[2]	18,002,000	18,002,000
Estimate of Fair Value Measurement [Member]
Securities available for sale	[1]	312,424,000	334,655,000
FHLBI stock	[2]	18,002,000	18,002,000
Fair Value, Inputs, Level 1 [Member]
Securities available for sale		0	0
Fair Value, Inputs, Level 1 [Member] | Reported Value Measurement [Member]
Cash		18,771,000	16,430,000
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Cash		18,771,000	16,430,000
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]
Cash equivalents		535,820,000	217,301,000
Loans held for sale		26,342,000	4,978,000
Mortgage servicing rights		7,103,000	4,652,000
Accrued interest receivable		11,025,000	9,944,000
Deposits		3,372,034,000	2,690,384,000
Repurchase agreements		157,017,000	102,675,000
FHLBI advances		394,000,000	354,000,000
Subordinated debentures		47,392,000	46,881,000
Accrued interest payable		2,447,000	3,949,000
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Cash equivalents		535,820,000	217,301,000
Loans held for sale		27,813,000	4,978,000
Mortgage servicing rights		9,161,000	7,375,000
Accrued interest receivable		11,025,000	9,944,000
Deposits		3,353,217,000	2,600,452,000
Repurchase agreements		157,017,000	102,675,000
FHLBI advances		412,940,000	361,887,000
Subordinated debentures		47,392,000	46,140,000
Accrued interest payable		2,447,000	3,949,000
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Loans, net		3,288,630,000	2,827,800,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Loans, net		$ 3,408,267,000	$ 2,887,168,000

[1] See Note 10 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.