Note 14 - Stockholders' Equity and Regulatory Requirements - Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Union Center National Bank [Member]
Leverage (Tier 1) capital	$ 1,074,204	$ 996,013
Leverage (Tier 1) capital, ratio	0.112	0.1064
Leverage (Tier 1) capital, capital adequacy	$ 383,619	$ 374,553
Leverage (Tier 1) capital, capital adequacy, ratio	0.04	0.04
Leverage (Tier 1) capital, well capitalized	$ 479,524	$ 468,191
Leverage (Tier 1) capital, well capitalized, ratio	0.05	0.05
CET one risk based capital	$ 1,074,204	$ 996,013
CET one risk based capital, ratio	0.1231	0.116
CET one risk based capital, capital adequacy	$ 392,643	$ 386,289
CET one risk based capital, capital adequacy, ratio	0.045	0.045
CET one risk based capital, well capitalized	$ 567,151	$ 557,972
CET one risk based capital, well capitalized, ratio	0.065	0.065
Tier 1, risk based capital	$ 1,074,204	$ 996,013
Tier 1, risk based capital, ratio	0.1231	0.116
Tier 1, risk based capital, capital adequacy	$ 523,524	$ 515,051
Tier 1, risk based capital, capital adequacy, ratio	0.06	0.06
Tier 1, risk based capital, well capitalized	$ 698,032	$ 686,735
Tier 1, risk based capital, well capitalized, ratio	0.08	0.08
Total capital	$ 1,158,572	$ 1,117,733
Total capital, ratio	0.1328	0.1302
Total capital, capital adequacy	$ 698,032	$ 686,735
Total capital, capital adequacy, ratio	0.08	0.08
Total capital, well capitalized	$ 872,540	$ 858,419
Total capital, well capitalized, ratio	0.10	0.10
Parent Company [Member]
Leverage (Tier 1) capital	$ 1,042,481	$ 1,000,577
Leverage (Tier 1) capital, ratio	0.1086	0.1068
Leverage (Tier 1) capital, capital adequacy	$ 383,900	$ 374,729
Leverage (Tier 1) capital, capital adequacy, ratio	0.04	0.04
CET one risk based capital	$ 926,399	$ 884,495
CET one risk based capital, ratio	0.1062	0.103
CET one risk based capital, capital adequacy	$ 392,650	$ 386,295
CET one risk based capital, capital adequacy, ratio	0.045	0.045
Tier 1, risk based capital	$ 1,042,481	$ 1,000,577
Tier 1, risk based capital, ratio	0.1195	0.1166
Tier 1, risk based capital, capital adequacy	$ 523,533	$ 515,061
Tier 1, risk based capital, capital adequacy, ratio	0.06	0.06
Total capital	$ 1,201,849	$ 1,240,047
Total capital, ratio	0.1377	0.1445
Total capital, capital adequacy	$ 698,044	$ 686,748
Total capital, capital adequacy, ratio	0.08	0.08