Note 8 - Loans - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Beginning Balance	$ 169,680	$ 122,651	$ 123,224	$ 122,391
Provision/(reversal) for possible credit losses	12,500	(2,000)	62,500	(2,000)
Charge-offs	(6,956)	(3,356)	(13,383)	(6,300)
Recoveries	3,906	8,613	6,789	11,817
Net (charge-offs)/recoveries	(3,050)	5,257	(6,594)	5,517
Ending Balance	179,130	125,908	179,130	125,908
Reserve for impaired loans	8,495	1,501	8,495	1,501
Reserve for non-impaired loans	170,635	124,407	170,635	124,407
Reserve for off-balance sheet credit commitments	5,663	4,550	5,663	4,550
Commercial Portfolio Segment [Member]
Beginning Balance	82,256	54,293	57,021	54,978
Provision/(reversal) for possible credit losses	298	7,400	29,402	8,262
Charge-offs	(6,956)	(3,356)	(13,383)	(6,300)
Recoveries	3,796	212	6,354	1,609
Net (charge-offs)/recoveries	(3,160)	(3,144)	(7,029)	(4,691)
Ending Balance	79,394	58,549	79,394	58,549
Reserve for impaired loans	7,704	744	7,704	744
Reserve for non-impaired loans	71,690	57,805	71,690	57,805
Reserve for off-balance sheet credit commitments	4,297	2,505	4,297	2,505
Real Estate Construction Portfolio Segment [Member]
Beginning Balance	26,700	21,010	19,474	19,626
Provision/(reversal) for possible credit losses	6,012	(2,690)	13,238	(2,540)
Charge-offs	0	0	0	0
Recoveries	0	3,378	0	4,612
Net (charge-offs)/recoveries	0	3,378	0	4,612
Ending Balance	32,712	21,698	32,712	21,698
Reserve for impaired loans	0	0	0	0
Reserve for non-impaired loans	32,712	21,698	32,712	21,698
Reserve for off-balance sheet credit commitments	896	1,608	896	1,608
Commercial Real Estate Portfolio Segment [Member]
Beginning Balance	41,132	33,154	33,602	33,487
Provision/(reversal) for possible credit losses	5,438	(4,648)	12,718	(5,234)
Charge-offs	0	0	0	0
Recoveries	95	4,961	345	5,214
Net (charge-offs)/recoveries	95	4,961	345	5,214
Ending Balance	46,665	33,467	46,665	33,467
Reserve for impaired loans	582	536	582	536
Reserve for non-impaired loans	46,083	32,931	46,083	32,931
Reserve for off-balance sheet credit commitments	172	121	172	121
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Beginning Balance	19,592	14,164	13,108	14,282
Provision/(reversal) for possible credit losses	752	(2,057)	7,161	(2,495)
Charge-offs	0	0	0	0
Recoveries	15	62	90	382
Net (charge-offs)/recoveries	15	62	90	382
Ending Balance	20,359	12,169	20,359	12,169
Reserve for impaired loans	209	221	209	221
Reserve for non-impaired loans	20,150	11,948	20,150	11,948
Reserve for off-balance sheet credit commitments	294	313	294	313
Installment and Other Loans [Member ]
Beginning Balance	0	30	19	18
Provision/(reversal) for possible credit losses	0	(5)	(19)	7
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net (charge-offs)/recoveries	0	0	0	0
Ending Balance	0	25	0	25
Reserve for impaired loans	0	0	0	0
Reserve for non-impaired loans	0	25	0	25
Reserve for off-balance sheet credit commitments	$ 4	$ 3	$ 4	$ 3