Note 10 - Fair Values of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($)		Jun. 30, 2018	Dec. 31, 2017
Financial assets:
Securities available for sale		$ 331,142,000	$ 335,744,000
Reported Value Measurement [Member]
Financial assets:
Securities available for sale	[1]	331,142,000	335,744,000
FHLBI stock	[2]	11,036,000	11,036,000
Reported Value Measurement [Member] | Interest Rate Swap [Member]
Financial liabilities:
Interest rate swap	[1]	0	2,000
Estimate of Fair Value Measurement [Member]
Financial assets:
Securities available for sale	[1]	331,142,000	335,744,000
FHLBI stock	[2]	11,036,000	11,036,000
Estimate of Fair Value Measurement [Member] | Interest Rate Swap [Member]
Financial liabilities:
Interest rate swap	[1]	0	2,000
Fair Value, Inputs, Level 1 [Member] | Reported Value Measurement [Member]
Financial assets:
Cash		11,471,000	11,565,000
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Financial assets:
Cash		11,471,000	11,565,000
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]
Financial assets:
Cash equivalents		114,269,000	188,536,000
Loans held for sale		3,063,000	2,553,000
Mortgage servicing rights		4,722,000	5,106,000
Accrued interest receivable		9,260,000	8,770,000
Financial liabilities:
Deposits		2,529,811,000	2,522,365,000
Repurchase agreements		94,573,000	118,748,000
FHLBI advances		230,000,000	220,000,000
Subordinated debentures		45,858,000	45,517,000
Accrued interest payable		1,853,000	1,919,000
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Financial assets:
Cash equivalents		114,269,000	188,536,000
Loans held for sale		3,063,000	2,553,000
Mortgage servicing rights		7,911,000	8,373,000
Accrued interest receivable		9,260,000	8,770,000
Financial liabilities:
Deposits		2,337,790,000	2,368,188,000
Repurchase agreements		94,573,000	118,748,000
FHLBI advances		223,073,000	217,130,000
Subordinated debentures		46,235,000	45,732,000
Accrued interest payable		1,853,000	1,919,000
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Financial assets:
Loans, net		2,612,626,000	2,536,498,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Financial assets:
Loans, net		$ 2,611,383,000	$ 2,520,063,000

[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.