Note 4 - Investment Securities (Details Textual) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2026 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Dec. 31, 2025 USD ($)
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ 1,682,820	$ 1,682,820		$ 1,658,223
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss	$ 2,300	$ 2,300		$ 3,000
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	101	101		159
Debt Securities, Available-for-Sale, Sold at Par Value	$ 160,200	$ 370,600
Debt Securities, Available-for-Sale, Realized Loss	10,600	26,200
Payments to Acquire Debt Securities, Available-for-Sale		1,300,335	$ 779,062
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Debt Securities, Available-for-Sale, Excluding Accrued Interest, Allowance for Credit Loss, Not to Sell before Recovery, Credit Loss, Previously Recorded, Expense (Reversal)		0
Collateralized Mortgage-Backed Securities [Member]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ 670,853	$ 670,853		$ 629,437
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	71	71		138
US Treasury Securities [Member]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ 936,464	$ 936,464		$ 828,193
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	19	19
Corporate Debt Securities [Member]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ 69,834	$ 69,834		$ 147,012
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	5	5		8
US Government Corporations and Agencies Securities [Member]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ 1,045	$ 1,045		$ 5,822
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	5	5		10
Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ 4,624	$ 4,624		$ 22,748
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	1	1		3
Higher-yielding Securities [Member]
Payments to Acquire Debt Securities, Available-for-Sale		$ 341,800
Asset Pledged as Collateral [Member] \| Public Deposits and Other Borrowings [Member]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ 19,400	$ 19,400		$ 22,800

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with interest rate reset through auction process, sold at par value.

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