Note 1 - Summary of Significant Accounting Policies (Details Textual)	12 Months Ended
	Dec. 31, 2019 USD ($)	Jan. 01, 2020 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 01, 2014 USD ($)
Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities	5
Number of Operating Segments	1
Loans and Leases Receivable, Deferred Income, Total	$ 500,000			$ 900,000
Interest Income on Commercial and Mortgage Loans Discontinued Period	90 days
Maximum Delinquency Period for Consumer and Credit Card Loans to be Charged Off	120 days
Repossessed Assets, Total	$ 500,000			800,000
Loans and Leases Receivable, Allowance, Ending Balance	23,889,000			22,380,000
Retained Earnings (Accumulated Deficit), Ending Balance	$ 107,831,000			$ 75,483,000
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset			$ 1,300,000
Operating Lease, Liability, Total			$ 1,300,000
Accounting Standards Update 2016-13 [Member] | Subsequent Event [Member]
Loans and Leases Receivable, Allowance, Ending Balance		$ (1,000,000)
Retained Earnings (Accumulated Deficit), Ending Balance		$ 800,000
Core Deposits [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	5 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	33 years
Furniture and Fixtures [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Furniture and Fixtures [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	7 years
Firstbank Corporation [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets, Total					$ 1,500,000,000
Business Combination Branches Acquired					46