Note 15 - Stockholders' Equity and Regulatory Requirements - Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Details) $ in Thousands	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Union Center National Bank [Member]
Leverage (Tier 1) capital	$ 1,109,149	$ 1,074,204
Leverage (Tier 1) capital, ratio	0.1166	0.112
Leverage (Tier 1) capital, capital adequacy	$ 380,444	$ 383,619
Leverage (Tier 1) capital, capital adequacy, ratio	0.04	0.04
Leverage (Tier 1) capital, well capitalized	$ 475,555	$ 479,524
Leverage (Tier 1) capital, well capitalized, ratio	0.05	0.05
CET one risk based capital	$ 1,109,149	$ 1,074,204
CET one risk based capital, ratio	0.1263	0.1231
CET one risk based capital, capital adequacy	$ 395,068	$ 392,643
CET one risk based capital, capital adequacy, ratio	0.045	0.045
CET one risk based capital, well capitalized	$ 570,654	$ 567,151
CET one risk based capital, well capitalized, ratio	0.065	0.065
Tier 1, risk based capital	$ 1,109,149	$ 1,074,204
Tier 1, risk based capital, ratio	0.1263	0.1231
Tier 1, risk based capital, capital adequacy	$ 526,757	$ 523,524
Tier 1, risk based capital, capital adequacy, ratio	0.06	0.06
Tier 1, risk based capital, well capitalized	$ 702,343	$ 698,032
Tier 1, risk based capital, well capitalized, ratio	0.08	0.08
Total capital	$ 1,194,249	$ 1,158,572
Total capital, ratio	0.136	0.1328
Total capital, capital adequacy	$ 702,343	$ 698,032
Total capital, capital adequacy, ratio	0.08	0.08
Total capital, well capitalized	$ 877,929	$ 872,540
Total capital, well capitalized, ratio	0.10	0.10
Parent Company [Member]
Leverage (Tier 1) capital	$ 1,079,011	$ 1,042,481
Leverage (Tier 1) capital, ratio	0.1133	0.1086
Leverage (Tier 1) capital, capital adequacy	$ 380,796	$ 383,900
Leverage (Tier 1) capital, capital adequacy, ratio	0.04	0.04
CET one risk based capital	$ 962,929	$ 926,399
CET one risk based capital, ratio	0.1097	0.1062
CET one risk based capital, capital adequacy	$ 395,075	$ 392,650
CET one risk based capital, capital adequacy, ratio	0.045	0.045
Tier 1, risk based capital	$ 1,079,011	$ 1,042,481
Tier 1, risk based capital, ratio	0.1229	0.1195
Tier 1, risk based capital, capital adequacy	$ 526,767	$ 523,533
Tier 1, risk based capital, capital adequacy, ratio	0.06	0.06
Total capital	$ 1,239,111	$ 1,201,849
Total capital, ratio	0.1411	0.1377
Total capital, capital adequacy	$ 702,356	$ 698,044
Total capital, capital adequacy, ratio	0.08	0.08