Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015	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		$ 1,000	$ 1,400
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
Foreclosed Assets		$ 2,300	$ 500
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		35.00%	35.00%	35.00%
Reclassification from AOCI to Retained Earnings, Current Period		$ 0
Adjustments for New Accounting Principle, Early Adoption [Member]
Reclassification from AOCI to Retained Earnings, Current Period		$ 900
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Core Deposits [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years
Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life		5 years
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					$ 1,500,000
Business Combination Branches Acquired					46