Note 5 - Loans and the Allowance for Credit Losses (Details Textual) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Financing Receivable, after Allowance for Credit Loss	$ 8,075,826		$ 8,075,826		$ 8,263,171
Financing Receivable, Modified, Subsequent Default, Number of Contracts			0	0
Commercial Portfolio Segment [Member]
Financing Receivable, Trouble Debt Restructuring, Number of Contracts			2	1
Financing Receivable, Modified in Period, Amount	11,150	$ 0	$ 11,276	$ 53
Commercial Portfolio Segment [Member] | Six-month Term Extension [Member]
Financing Receivable, Modified in Period, Amount			11,100
Commercial Portfolio Segment [Member] | Three-month Payment Deferral [Member]
Financing Receivable, Modified in Period, Amount			$ 100
Commercial Portfolio Segment [Member] | Three Year Term Extension [Member]
Financing Receivable, Modified in Period, Amount				50
Commercial Portfolio Segment [Member] | Fifteen Year Term Extension [Member]
Financing Receivable, Modified in Period, Amount				$ 213
Residential Portfolio Segment [Member]
Financing Receivable, Trouble Debt Restructuring, Number of Contracts			1
Financing Receivable, Modified in Period, Amount	1,417		$ 1,417
Residential Portfolio Segment [Member] | Freezing of a Loan Commitment, Combined With a Ten-year Term Extension [Member]
Financing Receivable, Modified in Period, Amount			1,400
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Trouble Debt Restructuring, Number of Contracts				1
Financing Receivable, Modified in Period, Amount		$ 213		$ 213
Asset Pledged as Collateral [Member] | Federal Home Loan Bank Advances [Member]
Financing Receivable, after Allowance for Credit Loss	$ 5,700,000		$ 5,700,000		$ 5,800,000