Note 9 - Fair Value Measurement - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Estimated fair value	$ 148,180
Reported Value Measurement [Member]
Cash and cash equivalents	64,690	$ 87,537
Estimated fair value	148,180	137,466
Loans, net	485,171	482,248
FHLB stock	2,685	2,685
Accrued interest receivable	2,460	2,582
Deposits	652,791	662,657
Repurchase agreements	8,675	10,074
Junior subordinated deferrable interest debentures	10,310	10,310
Accrued interest payable	65	64
Estimate of Fair Value Measurement [Member]
Cash and cash equivalents	64,690	87,537
Estimated fair value	148,180	137,466
Loans, net	486,517	484,269
Accrued interest receivable	2,460	2,582
Deposits	652,809	662,678
Repurchase agreements	8,675	10,074
Junior subordinated deferrable interest debentures	8,065	7,829
Accrued interest payable	65	64
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	64,690	87,537
Accrued interest receivable	34	31
Deposits	610,354	616,617
Accrued interest payable	10	10
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Estimated fair value	148,180	137,466
Accrued interest receivable	501	522
Deposits	42,455	46,061
Repurchase agreements	8,675	10,074
Accrued interest payable	38	39
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Loans, net	486,517	484,269
Accrued interest receivable	1,925	2,029
Junior subordinated deferrable interest debentures	8,065	7,829
Accrued interest payable	$ 17	$ 15