Note 3 - Investment Securities - Credit Quality (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Debt securities held to maturity, amortized cost	$ 860,869	$ 878,397
AAA/AA/A [Member]
Debt securities held to maturity, amortized cost	654,654
BBB + [Member]
Debt securities held to maturity, amortized cost	204,984
NR [Member]
Debt securities held to maturity, amortized cost	1,231
Agency Residential MBS [Member]
Debt securities held to maturity, amortized cost	67,777	78,565
Agency Residential MBS [Member] | AAA/AA/A [Member]
Debt securities held to maturity, amortized cost	67,271
Agency Residential MBS [Member] | BBB + [Member]
Debt securities held to maturity, amortized cost	0
Agency Residential MBS [Member] | NR [Member]
Debt securities held to maturity, amortized cost	506
US States and Political Subdivisions Debt Securities [Member]
Debt securities held to maturity, amortized cost	61,043	71,182
US States and Political Subdivisions Debt Securities [Member] | AAA/AA/A [Member]
Debt securities held to maturity, amortized cost	60,318
US States and Political Subdivisions Debt Securities [Member] | BBB + [Member]
Debt securities held to maturity, amortized cost	0
US States and Political Subdivisions Debt Securities [Member] | NR [Member]
Debt securities held to maturity, amortized cost	725
Corporate Debt Securities [Member]
Debt securities held to maturity, amortized cost	732,049	$ 728,650
Corporate Debt Securities [Member] | AAA/AA/A [Member]
Debt securities held to maturity, amortized cost	527,065
Corporate Debt Securities [Member] | BBB + [Member]
Debt securities held to maturity, amortized cost	204,984
Corporate Debt Securities [Member] | NR [Member]
Debt securities held to maturity, amortized cost	$ 0