Note 1 - Nature of Business and Significant Accounting Policies (Details)	1 Months Ended		12 Months Ended
	Nov. 30, 2023 USD ($)	Nov. 30, 2022 USD ($)	Dec. 31, 2023 USD ($) subsidiary segment shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares
Number of subsidiaries commercial banks | subsidiary			4
Number of portfolio segments | segment			8
Financing Receivable, Lines of Credit Maximum Term			1 year
Minimum number of months of repayment performance to restore to accrual status, monthly payment loans			15 months
Minimum number of years of repayment performance to restore to accrual status, quarterly or semi-monthly payment loans			15 months
Number of Non-Consolidated Subsidiaries Issuing Trust Preferred Securities | subsidiary			7
Cash Reserve Deposit Required and Made			$ 0	$ 0
Goodwill, Impaired, Accumulated Impairment Loss			$ 1,000,000,000.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number | shares			233,967	295,077	318,266
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value			$ 7,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value			7,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value			440,000	$ 387,000	$ 419,000
Allocated Share-based Compensation Expense			2,678,000	2,438,000	2,352,000
Accrued investment income receivable			$ 31,800,000	$ 24,300,000
Goodwill impairment	$ 0	$ 0
Preferred Stock, Shares Authorized | shares			250,000	250,000
Preferred Stock, Shares Outstanding | shares			0	0
Minimum outstanding balance considered for calculation of low quality loans allowance on case-to-case basis			$ 250,000
Maximum principal balance considered for placing low quality loans in the unique pool			250,000
Other Assets
Accrued investment income receivable			31,800,000
Subsidiary banks with an asset size of $1.0 billion or less
Lending Threshold Requiring Additional Loan Review			1,000,000.0
Subsidiary banks with an asset size of over $1.0 billion
Lending Threshold Requiring Additional Loan Review			2,000,000.0
Employee Stock Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized			$ 566,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			1 year 9 months 7 days
Allocated Share-based Compensation Expense			$ 286,000	$ 246,000	270,000
In The Money Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number | shares			290,149
Restricted Stock
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized			$ 3,200,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			1 year 9 months 7 days
Allocated Share-based Compensation Expense			$ 2,084,000	$ 1,967,000	$ 1,864,000
Subsidiaries [Member] | Fixed Rate Residential Mortgage [Member]
Financing receivable, term			15 years
Commercial Portfolio Segment [Member]
Financing Receivable, Term Loans, Generally Maximum Term			7 years
Minimum
Financing Receivable, Lines of Credit Maximum Term			6 months
Residual Value Percent of Cost			3.00%
Minimum | Subsidiaries [Member] | Adjustable Rate Residential Mortgage [Member]
Financing receivable, term			1 year
Minimum | Commercial Portfolio Segment [Member] | Term Loan [Member]
Financing receivable, term			3 years
Maximum
Permanent loans term			20 years
Financing Receivable, Credit Weaknesses Borrowers, Term			365 days
Financing Receivable, Lines of Credit Maximum Term			1 year
Residual Value Percent of Cost			25.00%
Maximum | Subsidiaries [Member] | Adjustable Rate Residential Mortgage [Member]
Financing receivable, term			5 years
Maximum | Commercial Portfolio Segment [Member] | Term Loan [Member]
Financing receivable, term			5 years
Core Deposits [Member]
Estimated useful life			10 years