Note 9 - Long-term Debt (Details Textual) - USD ($) $ in Millions		1 Months Ended
	Dec. 01, 2023	Mar. 31, 2021	Nov. 30, 2018	Sep. 30, 2023	Dec. 31, 2022
Debt Instrument, Face Amount				$ 175	$ 175
Six Point One Eight Percent Fixed To Floating Rate Subordinated Debentures Due December First Two Thousands Twenty Eight [Member]
Debt Instrument, Face Amount			$ 55	55	55
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate			6.18%
Banking Regulation, Common Equity Tier One Risk-Based Capital, Actual			$ 25
Six Point One Eight Percent Fixed To Floating Rate Subordinated Debentures Due December First Two Thousands Twenty Eight [Member] | Forecast [Member]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	100.00%
Six Point One Eight Percent Fixed To Floating Rate Subordinated Debentures Due December First Two Thousands Twenty Eight [Member] | London Interbank Offered Rate [Member]
Debt Instrument, Basis Spread on Variable Rate			3.15%
Four Percent Fixed To Floating Rate Subordinated Debentures Due April First Two Thousand Thirty One [Member]
Debt Instrument, Face Amount		$ 120		$ 120	$ 120
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate		4.00%
Four Percent Fixed To Floating Rate Subordinated Debentures Due April First Two Thousand Thirty One [Member] | Secured Overnight Financing Rate (SOFR) [Member]
Debt Instrument, Basis Spread on Variable Rate		3.29%