Note 6 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Gross loans	$ 11,739,093	$ 11,457,558
Nonaccrual	41,579	45,915
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	95,155	21,882
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	8,009
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	7,960	17,472
Financial Asset, Past Due [Member]
Gross loans	144,694	93,278
Financial Asset, Not Past Due [Member]
Gross loans	11,594,399	11,364,280
Commercial Portfolio Segment [Member]
Gross loans	1,644,836	1,565,963
Nonaccrual	12,798	13,039
Commercial Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	2,881	875
Commercial Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	539
Commercial Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	426	427
Commercial Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Gross loans	16,105	14,880
Commercial Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	1,628,731	1,551,083
Commercial Real Estate Portfolio Segment [Member]
Gross loans	8,318,844	8,054,696
Nonaccrual	24,935	28,561
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	82,614	13,602
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	6,098
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	6,765	16,276
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Gross loans	114,314	64,537
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	8,204,530	7,990,159
Commercial Construction Portfolio Segment [Member]
Gross loans	571,073	623,902
Nonaccrual	0	0
Commercial Construction Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	0	0
Commercial Construction Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	0
Commercial Construction Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Commercial Construction Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Gross loans	0	0
Commercial Construction Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	571,073	623,902
Residential Portfolio Segment [Member]
Gross loans	1,202,539	1,210,980
Nonaccrual	3,846	4,315
Residential Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	9,660	7,405
Residential Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	1,372
Residential Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	769	769
Residential Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Gross loans	14,275	13,861
Residential Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	1,188,264	1,197,119
Consumer Portfolio Segment [Member]
Gross loans	1,801	2,017
Nonaccrual	0	0
Consumer Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	$ 1,801	$ 2,017