Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands		1 Months Ended	12 Months Ended
	Jan. 01, 2022 USD ($)	Apr. 30, 2020	Dec. 31, 2021 USD ($)	May 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Aug. 08, 2020 USD ($)	Jul. 15, 2020 USD ($)	Jun. 01, 2014 USD ($)
Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities			5
Loans and Leases Receivable, Deferred Income, Total			$ 2,500		$ 4,400
Interest Income on Commercial and Mortgage Loans Discontinued Period (Day)			90 days
Maximum Delinquency Period for Consumer and Credit Card Loans to be Charged Off (Day)			120 days
Repossessed Assets, Total			$ 0		700
Subsequent Event [Member] | Minimum [Member]
Financing Receivable, Allowance for Credit Loss, Allowance Reduction	$ 200
Subsequent Event [Member] | Maximum [Member]
Financing Receivable, Allowance for Credit Loss, Allowance Reduction	$ 2,000
Core Deposits [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (Year)			10 years
Not Designated as Hedging Instrument [Member] | Mortgage Loan Derivative [Member]
Derivative Asset, Total			$ 300		500
Commercial Loan [Member]
Loan Participation, Amount			24,200		$ 18,100
Commercial Portfolio Segment [Member]
Financing Receivable, Payment Deferrals, Interest-only Amendments, Period (Day)		90 days
Financing Receivable, Payment Deferrals, Principal and Interest, Period (Day)		90 days
Financing Receivable, Payment Deferrals, Interest Rate		0.00%
Financing Receivable, Number of Principal and Interest Payment Deferrals								750
Financing Receivable, Principal and Interest Deferred Payments			$ 0					$ 719,000
Retail Portfolio Segment [Member]
Financing Receivable, Payment Deferrals, Principal and Interest, Period (Day)		90 days
Financing Receivable, Number of Principal and Interest Payment Deferrals			8			260
Financing Receivable, Principal and Interest Deferred Payments			$ 400			$ 23,800
SBA, CARES Act, Paycheck Protection Program [Member]
Number of Loans Originated Under the Paycheck Protection Program							2,200
Financing Receivable, before Allowance for Credit Loss, Total							$ 554,000
Financing Receivable, Not Yet Forgiven, Number of Loans			10
Financing Receivable, Not Yet Forgiven			$ 1,300
Amortization of Deferred Loan Origination Fees, Net			3,700
SBA, CARES Act, Paycheck Protection Program, Round Two [Member]
Number of Loans Originated Under the Paycheck Protection Program				1,200
Financing Receivable, before Allowance for Credit Loss, Total				$ 208,000
Amortization of Deferred Loan Origination Fees, Net			$ 7,100
Financing Receivable, Forgiveness Transactions, Number of Loans			1,000
Financing Receivable, Forgiveness Transactions			$ 169,000
Firstbank Corporation [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets, Total									$ 1,500,000
Business Combination Branches Acquired									46