Note 5 - Loans and the Allowance for Credit Losses - Loans by Origination and Risk Designation (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Originated Current Fiscal Year	$ 74,321		$ 444,378
Originated One Year Prior	427,604		1,873,427
Originated Two Years Prior	1,869,141		1,891,130
Originated Three Years Prior	1,861,663		419,300
Originated Four Years Prior	408,966		389,442
Originated Five or More Years Prior	1,802,395		1,497,749
Revolving Loans	1,860,011		1,836,415
Gross loans	8,304,101		8,351,841
Gross write-off, current year	0		54
Gross write-off, one year prior	0		3,397
Gross write-off, two years prior	300		0
Gross write-off, three years prior	0		0
Gross write-off, four years prior	0		280
Gross write-off, five years prior	2,885		13,236
Gross write-off, revolving	0		82
Gross write-off	3,185	$ 4,484	17,049
Pass [Member]
Originated Current Fiscal Year	74,321		444,128
Originated One Year Prior	427,354		1,862,368
Originated Two Years Prior	1,858,330		1,888,446
Originated Three Years Prior	1,859,002		419,299
Originated Four Years Prior	408,948		387,013
Originated Five or More Years Prior	1,741,426		1,435,499
Revolving Loans	1,827,238		1,802,411
Gross loans	8,196,619		8,239,164
Special Mention [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		10,620
Originated Two Years Prior	10,687		0
Originated Three Years Prior	0		0
Originated Four Years Prior	18		562
Originated Five or More Years Prior	27,315		28,270
Revolving Loans	14,694		14,716
Gross loans	52,714		54,168
Substandard [Member]
Originated Current Fiscal Year	0		250
Originated One Year Prior	250		439
Originated Two Years Prior	124		2,684
Originated Three Years Prior	2,661		1
Originated Four Years Prior	0		1,867
Originated Five or More Years Prior	33,654		33,980
Revolving Loans	18,079		19,288
Gross loans	54,768		58,509
Doubtful [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Commercial Portfolio Segment [Member]
Originated Current Fiscal Year	8,719		178,832
Originated One Year Prior	163,879		263,210
Originated Two Years Prior	264,701		265,946
Originated Three Years Prior	257,635		38,910
Originated Four Years Prior	37,530		14,900
Originated Five or More Years Prior	129,219		127,257
Revolving Loans	710,811		689,675
Gross loans	1,572,494		1,578,730
Gross write-off, current year	0		54
Gross write-off, one year prior	0		3,397
Gross write-off, two years prior	300		0
Gross write-off, three years prior	0		0
Gross write-off, four years prior	0		280
Gross write-off, five years prior	0		11,094
Gross write-off, revolving	0		63
Gross write-off	300	2,767	14,888
Commercial Portfolio Segment [Member] | Pass [Member]
Originated Current Fiscal Year	8,719		178,582
Originated One Year Prior	163,629		252,151
Originated Two Years Prior	253,890		265,705
Originated Three Years Prior	257,399		38,909
Originated Four Years Prior	37,512		13,726
Originated Five or More Years Prior	112,276		112,145
Revolving Loans	706,574		684,779
Gross loans	1,539,999		1,545,997
Commercial Portfolio Segment [Member] | Special Mention [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		10,620
Originated Two Years Prior	10,687		0
Originated Three Years Prior	0		0
Originated Four Years Prior	18		562
Originated Five or More Years Prior	3,945		3,417
Revolving Loans	3,184		3,199
Gross loans	17,834		17,798
Commercial Portfolio Segment [Member] | Substandard [Member]
Originated Current Fiscal Year	0		250
Originated One Year Prior	250		439
Originated Two Years Prior	124		241
Originated Three Years Prior	236		1
Originated Four Years Prior	0		612
Originated Five or More Years Prior	12,998		11,695
Revolving Loans	1,053		1,697
Gross loans	14,661		14,935
Commercial Portfolio Segment [Member] | Doubtful [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Commercial Real Estate Portfolio Segment [Member]
Originated Current Fiscal Year	55,180		248,660
Originated One Year Prior	247,846		1,561,841
Originated Two Years Prior	1,557,645		1,586,997
Originated Three Years Prior	1,566,041		352,445
Originated Four Years Prior	343,799		354,646
Originated Five or More Years Prior	1,563,877		1,276,583
Revolving Loans	495,562		514,373
Gross loans	5,829,950		5,895,545
Gross write-off, current year	0		0
Gross write-off, one year prior	0		0
Gross write-off, two years prior	0		0
Gross write-off, three years prior	0		0
Gross write-off, four years prior	0		0
Gross write-off, five years prior	2,885		2,142
Gross write-off, revolving	0		0
Gross write-off	2,885	1,717	2,142
Commercial Real Estate Portfolio Segment [Member] | Pass [Member]
Originated Current Fiscal Year	55,180		248,660
Originated One Year Prior	247,846		1,561,841
Originated Two Years Prior	1,557,645		1,585,109
Originated Three Years Prior	1,564,163		352,445
Originated Four Years Prior	343,799		353,391
Originated Five or More Years Prior	1,521,233		1,232,240
Revolving Loans	478,777		497,588
Gross loans	5,768,643		5,831,274
Commercial Real Estate Portfolio Segment [Member] | Special Mention [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	22,723		24,202
Revolving Loans	0		0
Gross loans	22,723		24,202
Commercial Real Estate Portfolio Segment [Member] | Substandard [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		1,888
Originated Three Years Prior	1,878		0
Originated Four Years Prior	0		1,255
Originated Five or More Years Prior	19,921		20,141
Revolving Loans	16,785		16,785
Gross loans	38,584		40,069
Commercial Real Estate Portfolio Segment [Member] | Doubtful [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Commercial Construction Portfolio Segment [Member]
Originated Current Fiscal Year	5,250		582
Originated One Year Prior	582		5,463
Originated Two Years Prior	4,201		15,645
Originated Three Years Prior	15,608		6,236
Originated Four Years Prior	6,236		0
Originated Five or More Years Prior	0		0
Revolving Loans	614,716		592,570
Gross loans	646,593		620,496
Gross write-off, current year	0		0
Gross write-off, one year prior	0		0
Gross write-off, two years prior	0		0
Gross write-off, three years prior	0		0
Gross write-off, four years prior	0		0
Gross write-off, five years prior	0		0
Gross write-off, revolving	0		0
Gross write-off	0	(0)	0
Commercial Construction Portfolio Segment [Member] | Pass [Member]
Originated Current Fiscal Year	5,250		582
Originated One Year Prior	582		5,463
Originated Two Years Prior	4,201		15,645
Originated Three Years Prior	15,608		6,236
Originated Four Years Prior	6,236		0
Originated Five or More Years Prior	0		0
Revolving Loans	606,016		583,870
Gross loans	637,893		611,796
Commercial Construction Portfolio Segment [Member] | Special Mention [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	8,700		8,700
Gross loans	8,700		8,700
Commercial Construction Portfolio Segment [Member] | Substandard [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Commercial Construction Portfolio Segment [Member] | Doubtful [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Residential Portfolio Segment [Member]
Originated Current Fiscal Year	4,466		15,455
Originated One Year Prior	15,268		42,830
Originated Two Years Prior	42,558		22,542
Originated Three Years Prior	22,379		21,704
Originated Four Years Prior	21,396		19,896
Originated Five or More Years Prior	109,299		93,909
Revolving Loans	38,848		39,705
Gross loans	254,214		256,041
Gross write-off, current year	0		0
Gross write-off, one year prior	0		0
Gross write-off, two years prior	0		0
Gross write-off, three years prior	0		0
Gross write-off, four years prior	0		0
Gross write-off, five years prior	0		0
Gross write-off, revolving	0		18
Gross write-off	0	(0)	18
Residential Portfolio Segment [Member] | Pass [Member]
Originated Current Fiscal Year	4,466		15,455
Originated One Year Prior	15,268		42,830
Originated Two Years Prior	42,558		21,987
Originated Three Years Prior	21,832		21,704
Originated Four Years Prior	21,396		19,896
Originated Five or More Years Prior	107,917		91,114
Revolving Loans	35,797		36,082
Gross loans	249,234		249,068
Residential Portfolio Segment [Member] | Special Mention [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	647		651
Revolving Loans	2,810		2,817
Gross loans	3,457		3,468
Residential Portfolio Segment [Member] | Substandard [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		555
Originated Three Years Prior	547		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	735		2,144
Revolving Loans	241		806
Gross loans	1,523		3,505
Residential Portfolio Segment [Member] | Doubtful [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Consumer Portfolio Segment [Member]
Originated Current Fiscal Year	706		849
Originated One Year Prior	29		83
Originated Two Years Prior	36		0
Originated Three Years Prior	0		5
Originated Four Years Prior	5		0
Originated Five or More Years Prior	0		0
Revolving Loans	74		92
Gross loans	850		1,029
Gross write-off, current year	0		0
Gross write-off, one year prior	0		0
Gross write-off, two years prior	0		0
Gross write-off, three years prior	0		0
Gross write-off, four years prior	0		0
Gross write-off, five years prior	0		0
Gross write-off, revolving	0		1
Gross write-off	0	$ (0)	1
Consumer Portfolio Segment [Member] | Pass [Member]
Originated Current Fiscal Year	706		849
Originated One Year Prior	29		83
Originated Two Years Prior	36		0
Originated Three Years Prior	0		5
Originated Four Years Prior	5		0
Originated Five or More Years Prior	0		0
Revolving Loans	74		92
Gross loans	850		1,029
Consumer Portfolio Segment [Member] | Special Mention [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Consumer Portfolio Segment [Member] | Substandard [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	0		0
Consumer Portfolio Segment [Member] | Doubtful [Member]
Originated Current Fiscal Year	0		0
Originated One Year Prior	0		0
Originated Two Years Prior	0		0
Originated Three Years Prior	0		0
Originated Four Years Prior	0		0
Originated Five or More Years Prior	0		0
Revolving Loans	0		0
Gross loans	$ 0		$ 0