Note 4 - Loans and Allowance for Loan Losses - Loans Modified As Troubled Debt Restructurings Within the Previous Twelve Months That Became Over 30 Days Past Due (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Originated Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Commercial Portfolio Segment [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Retail Portfolio Segment [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Originated Loan [Member] | Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Acquired Loan [Member]
Number of Contracts	3	0
Recorded Principal Balance	$ 216,000	$ 0
Acquired Loan [Member] | Commercial Portfolio Segment [Member]
Number of Contracts	1	0
Recorded Principal Balance	$ 114,000	$ 0
Acquired Loan [Member] | Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Number of Contracts	1	0
Recorded Principal Balance	$ 114,000	$ 0
Acquired Loan [Member] | Commercial Portfolio Segment [Member] | Vacant Land and Land Development and Residential Construction Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Acquired Loan [Member] | Commercial Portfolio Segment [Member] | Real Estate Owner Occupied Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Acquired Loan [Member] | Commercial Portfolio Segment [Member] | Real Estate Non Owner Occupied Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Acquired Loan [Member] | Commercial Portfolio Segment [Member] | Real Estate Multi Family and Residential Rental Loan [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0
Acquired Loan [Member] | Retail Portfolio Segment [Member]
Number of Contracts	2	0
Recorded Principal Balance	$ 102,000	$ 0
Acquired Loan [Member] | Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Number of Contracts	2	0
Recorded Principal Balance	$ 102,000	$ 0
Acquired Loan [Member] | Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Number of Contracts	0	0
Recorded Principal Balance	$ 0	$ 0