Note 3 - Loans and Allowance for Credit Losses on Loans (Details Textual) - USD ($)		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financing Receivable, Accrued Interest, after Allowance for Credit Loss		$ 22,000,000		$ 21,000,000
Financing Receivable, before Allowance for Credit Loss	[1]	5,849,715,000		5,771,038,000
Loans and Leases Receivable, Related Parties		62,000,000		62,000,000
Financing Receivable, Nonaccrual, Interest Income		0	$ 0
Mortgage Loans in Process of Foreclosure, Amount		112,000		668,000
Asset Pledged as Collateral [Member] | Federal Home Loan Bank Advances [Member]
Financing Receivable, before Allowance for Credit Loss		$ 3,210,000,000		$ 3,150,000,000

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