Note 4 - Loans and Allowance for Loan Losses (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Payments to Acquire Loans Receivable	$ 2,830	$ 2,512	$ 8,613
Loans Receivable Acquired, Average Amount Outstanding	123	120
Loans and Leases Receivable, Related Parties	13,124	13,499
Allowance for Credit Losses, Change in Method of Calculating Impairment	1,800	2,000
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 0	$ 0
Financing Receivable, Modifications, Number of Contracts	0	0
Allowance for Loan Losses, Look-back Period	12	16
Directors, Executive Officers, Principal Shareholders, and Immediate Family Members [Member]
Loans and Leases Receivable, Related Parties	$ 13,100