Note 3 - Debt Securities Available for Sale and Held to Maturity - Credit Quality (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Held to Maturity, Amortized Cost	$ 799,559	$ 819,575
AAA/AA/A [Member]
Held to Maturity, Amortized Cost	645,038
BBB+/BBB [Member]
Held to Maturity, Amortized Cost	154,090
NR [Member]
Held to Maturity, Amortized Cost	431
Agency Residential MBS [Member]
Held to Maturity, Amortized Cost	41,271	43,734
Agency Residential MBS [Member] \| AAA/AA/A [Member]
Held to Maturity, Amortized Cost	40,840
Agency Residential MBS [Member] \| BBB+/BBB [Member]
Held to Maturity, Amortized Cost	0
Agency Residential MBS [Member] \| NR [Member]
Held to Maturity, Amortized Cost	431
US States and Political Subdivisions Debt Securities [Member]
Held to Maturity, Amortized Cost	26,120	33,597
US States and Political Subdivisions Debt Securities [Member] \| AAA/AA/A [Member]
Held to Maturity, Amortized Cost	26,120
US States and Political Subdivisions Debt Securities [Member] \| BBB+/BBB [Member]
Held to Maturity, Amortized Cost	0
US States and Political Subdivisions Debt Securities [Member] \| NR [Member]
Held to Maturity, Amortized Cost	0
Corporate Debt Securities [Member]
Held to Maturity, Amortized Cost	732,168	$ 742,244
Corporate Debt Securities [Member] \| AAA/AA/A [Member]
Held to Maturity, Amortized Cost	578,078
Corporate Debt Securities [Member] \| BBB+/BBB [Member]
Held to Maturity, Amortized Cost	154,090
Corporate Debt Securities [Member] \| NR [Member]
Held to Maturity, Amortized Cost	$ 0