Note 4 - Loans and Allowance for Loan Losses (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance	$ 11.9	$ 15.5
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	5.2	6.2
Impaired Financing Receivable, Interest Income, Accrual Method	0.4	1.2	$ 2.4
Impaired Financing Receivable, Interest Income, Cash Basis Method	0.5	0.1	1.7
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	$ 0.3	$ 0.1	$ 0.3
Minimum Number of Days Past Due at Period End For Loans Modified as Troubled Debt Restructurings	30 days