Note 17 - Fair Values of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities		$ 335,744,000	$ 328,060,000
Servicing Asset at Fair Value, Amount		8,400,000	8,000,000
Reported Value Measurement [Member]
Available-for-sale Securities	[1]	335,744,000	328,060,000
Federal Home Loan Bank stock	[2]	11,036,000	8,026,000
Securities sold under agreements to repurchase		118,748,000	131,710,000
Federal Home Loan Bank advances		220,000,000	175,000,000
Reported Value Measurement [Member] | Interest Rate Swap [Member]
Interest rate swap	[1]	2,000	84,000
Estimate of Fair Value Measurement [Member]
Available-for-sale Securities	[1]	335,744,000	328,060,000
Federal Home Loan Bank stock	[2]	11,036,000	8,026,000
Securities sold under agreements to repurchase		118,748,000	131,710,000
Federal Home Loan Bank advances		217,130,000	174,734,000
Estimate of Fair Value Measurement [Member] | Interest Rate Swap [Member]
Interest rate swap	[1]	2,000	84,000
Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities		0
Fair Value, Inputs, Level 1 [Member] | Reported Value Measurement [Member]
Cash		11,565,000	11,493,000
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Cash		11,565,000	11,493,000
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]
Cash equivalents		188,536,000	172,103,000
Loans held for sale		2,553,000	1,035,000
Servicing Asset at Fair Value, Amount		5,106,000	5,544,000
Accrued interest receivable		8,770,000	7,714,000
Deposits		2,522,365,000	2,374,985,000
Subordinated debentures		45,517,000	44,835,000
Accrued interest payable		1,919,000	1,592,000
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Cash equivalents		188,536,000	172,103,000
Loans held for sale		2,553,000	1,035,000
Servicing Asset at Fair Value, Amount		8,373,000	7,997,000
Accrued interest receivable		8,770,000	7,714,000
Deposits		2,368,188,000	2,286,548,000
Subordinated debentures		45,732,000	45,220,000
Accrued interest payable		1,919,000	1,592,000
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Loans, net		2,536,498,000	2,359,624,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Loans, net		$ 2,520,063,000	$ 2,353,276,000

[1] See Note 18 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.