Note 5 - Loans and ACL for Loans (Details Textual)		12 Months Ended
		Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Loans and Leases Receivable, Deferred Expense (Income)		$ 2,000,000	$ 1,000,000
Continuing Involvement with Transferred Financial Assets, Principal Amount Outstanding		4,000,000	5,000,000
Financing Receivable, Accrued Interest, after Allowance for Credit Loss		21,000,000	17,000,000
Financing Receivable, before Allowance for Credit Loss	[1]	5,771,038,000	5,205,918,000
Financing Receivable, after Allowance for Credit Loss		5,691,664,000	5,132,387,000
Financing Receivable, Purchased with Credit Deterioration, Interest Income		5,000,000	5,200,000
Financing Receivable, Nonaccrual, Interest Income		0	0
Mortgage Loans in Process of Foreclosure, Amount		668,000	$ 317,000
Financing Receivable, Modifications, Number of Contracts			0
Financing Receivable, Troubled Debt Restructuring			$ 850,000
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts			0
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, before Allowance for Credit Loss		2,469,113,000	$ 2,231,975,000
Financing Receivable, Modifications, Number of Contracts			1
Financing Receivable, Troubled Debt Restructuring			$ 850,000
Acquisition of Commonwealth [Member] | Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable, after Allowance for Credit Loss		53,000,000
Asset Pledged as Collateral [Member] | Federal Home Loan Bank Advances [Member]
Financing Receivable, before Allowance for Credit Loss		$ 3,150,000,000	$ 2,770,000,000

[1] Total loans are presented inclusive of premiums, discounts and net loan origination fees and costs.