Note 7 - Fair Value Measurements - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Securities available for sale	$ 276,937,000	$ 255,844,000
Securities held to maturity	1,000	2,000
Reported Value Measurement [Member]
Cash and cash equivalents	24,798,000	45,835,000
Interest-bearing time deposits	10,295,000	14,735,000
Securities available for sale	276,937,000	255,844,000
Securities held to maturity	1,000	2,000
Loans held for sale	1,000,000	4,507,000
Loans, net	400,762,000	381,154,000
FHLB and other stock	1,979,000	1,650,000
Accrued interest receivable	2,595,000	2,363,000
Deposits	665,512,000	664,650,000
Advances from FHLB	4,000
Accrued interest payable	109,000	133,000
Estimate of Fair Value Measurement [Member]
Cash and cash equivalents	24,798,000	45,835,000
Interest-bearing time deposits	10,302,000	14,786,000
Securities available for sale	276,937,000	255,844,000
Securities held to maturity	1,000	2,000
Loans held for sale	1,020,000	4,598,000
Loans, net	400,430,000	381,459,000
FHLB and other stock	1,979,000	1,650,000
Accrued interest receivable	2,595,000	2,363,000
Deposits	664,553,000	663,806,000
Advances from FHLB	4,000
Accrued interest payable	109,000	133,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	24,798,000	45,835,000
Interest-bearing time deposits	0	0
Securities available for sale	211,000	74,000
Securities held to maturity	0	0
Loans held for sale	0	0
Loans, net	0	0
FHLB and other stock	0	0
Accrued interest receivable	0	0
Deposits	0	0
Advances from FHLB	0
Accrued interest payable	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Interest-bearing time deposits	10,302,000	14,786,000
Securities available for sale	276,726,000	255,770,000
Securities held to maturity	1,000	2,000
Loans held for sale	1,020,000	4,598,000
Loans, net	0	0
FHLB and other stock	1,979,000	1,650,000
Accrued interest receivable	2,595,000	2,363,000
Deposits	0	0
Advances from FHLB	4,000
Accrued interest payable	109,000	133,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0	0
Interest-bearing time deposits	0	0
Securities available for sale	0	0
Securities held to maturity	0	0
Loans held for sale	0	0
Loans, net	400,430,000	381,459,000
FHLB and other stock	0	0
Accrued interest receivable	0	0
Deposits	664,553,000	663,806,000
Advances from FHLB	0
Accrued interest payable	$ 0	$ 0