Note 8 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Loans held for investment	$ 19,429,396	$ 19,548,140
Recorded investment	98,107	66,681
Financial Asset, 30 to 59 Days Past Due [Member]
Loans held for investment	112,864	124,698
Financial Asset, 60 to 89 Days Past Due [Member]
Loans held for investment	36,331	38,941
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans held for investment	7,560	7,157
Financial Asset, Past Due [Member]
Loans held for investment	254,862	237,477
Recorded investment	98,107	66,681
Financial Asset, Not Past Due [Member]
Loans held for investment	19,174,534	19,310,663
Commercial Portfolio Segment [Member]
Loans held for investment	3,132,580	3,305,048
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans held for investment	25,777	11,771
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans held for investment	21,857	7,770
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans held for investment	6,060	508
Commercial Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans held for investment	68,336	34,453
Recorded investment	14,642	14,404
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans held for investment	3,064,244	3,270,595
Real Estate Construction Portfolio Segment [Member]
Loans held for investment	382,775	422,647
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans held for investment	0	25,389
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans held for investment	0	22,998
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans held for investment	0	0
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans held for investment	22,998	56,123
Recorded investment	22,998	7,736
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans held for investment	359,777	366,524
Commercial Real Estate Portfolio Segment [Member]
Loans held for investment	9,821,807	9,729,581
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans held for investment	25,684	27,900
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans held for investment	13,803	1,503
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans held for investment	1,500	6,649
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans held for investment	88,452	68,082
Recorded investment	47,465	32,030
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans held for investment	9,733,355	9,661,499
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans held for investment	6,087,068	6,084,666
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans held for investment	61,403	59,606
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans held for investment	671	6,670
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans held for investment	0	0
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans held for investment	75,076	78,787
Recorded investment	13,002	12,511
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans held for investment	6,011,992	6,005,879
Installment and Other Loans [Member ]
Loans held for investment	5,166	6,198
Installment and Other Loans [Member ] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans held for investment	0	32
Installment and Other Loans [Member ] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans held for investment	0	0
Installment and Other Loans [Member ] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans held for investment	0	0
Installment and Other Loans [Member ] | Financial Asset, Past Due [Member]
Loans held for investment	0	32
Recorded investment	0	0
Installment and Other Loans [Member ] | Financial Asset, Not Past Due [Member]
Loans held for investment	$ 5,166	$ 6,166