Note 2 - Investment Securities - Credit Quality (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Held to maturity	$ 878,397	$ 915,914
AAA/AA/A [Member]
Held to maturity	655,602
BBB + [Member]
Held to maturity	222,142
B- [Member]
Held to maturity	653
NR [Member]
Held to maturity	878,397
Agency Residential MBS [Member]
Held to maturity	78,565	104,852
Agency Residential MBS [Member] | AAA/AA/A [Member]
Held to maturity	78,092
Agency Residential MBS [Member] | BBB + [Member]
Held to maturity	0
Agency Residential MBS [Member] | B- [Member]
Held to maturity	473
Agency Residential MBS [Member] | NR [Member]
Held to maturity	78,565
US States and Political Subdivisions Debt Securities [Member]
Held to maturity	71,182	89,208
US States and Political Subdivisions Debt Securities [Member] | AAA/AA/A [Member]
Held to maturity	71,002
US States and Political Subdivisions Debt Securities [Member] | BBB + [Member]
Held to maturity	0
US States and Political Subdivisions Debt Securities [Member] | B- [Member]
Held to maturity	180
US States and Political Subdivisions Debt Securities [Member] | NR [Member]
Held to maturity	71,182
Corporate Debt Securities [Member]
Held to maturity	728,650	$ 721,854
Corporate Debt Securities [Member] | AAA/AA/A [Member]
Held to maturity	506,508
Corporate Debt Securities [Member] | BBB + [Member]
Held to maturity	222,142
Corporate Debt Securities [Member] | B- [Member]
Held to maturity	0
Corporate Debt Securities [Member] | NR [Member]
Held to maturity	$ 728,650