Note 4 - Loans - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance at beginning of year				$ 123,224				$ 122,391	$ 123,224	$ 122,391	$ 123,279
Provision/(reversal) for loan losses	$ (5,000)	$ 12,500	$ 25,000	25,000	$ (5,000)	$ (2,000)	$ 0	0	57,500	(7,000)	(4,500)
Charge-offs									(21,996)	(6,997)	(3,206)
Recoveries									7,810	14,830	6,818
Net (Charge-offs)/Recoveries									(14,186)	7,833
Balance at end of year	166,538				123,224				166,538	123,224	122,391
Reserve for impaired loans	6,429				3,236				6,429	3,236
Reserve for non-impaired loans	160,109				119,988				160,109	119,988
Reserve for off-balance sheet credit commitments	5,880				3,855				5,880	3,855
Commercial Portfolio Segment [Member]
Balance at beginning of year				57,021				54,978	57,021	54,978
Provision/(reversal) for loan losses									26,450	4,885
Charge-offs									(21,996)	(6,997)
Recoveries									7,267	4,155
Net (Charge-offs)/Recoveries									(14,729)	(2,842)
Balance at end of year	68,742				57,021				68,742	57,021	54,978
Reserve for impaired loans	1,030				2,543				1,030	2,543
Reserve for non-impaired loans	67,712				54,478				67,712	54,478
Reserve for off-balance sheet credit commitments	4,802				2,301				4,802	2,301
Real Estate Construction Portfolio Segment [Member]
Balance at beginning of year				19,474				19,626	19,474	19,626
Provision/(reversal) for loan losses									11,380	(4,764)
Charge-offs									0	0
Recoveries									0	4,612
Net (Charge-offs)/Recoveries									0	4,612
Balance at end of year	30,854				19,474				30,854	19,474	19,626
Reserve for impaired loans	0				0				0	0
Reserve for non-impaired loans	30,854				19,474				30,854	19,474
Reserve for off-balance sheet credit commitments	690				1,047				690	1,047
Commercial Real Estate Portfolio Segment [Member]
Balance at beginning of year				33,602				33,487	33,602	33,487
Provision/(reversal) for loan losses									15,164	(5,216)
Charge-offs									0	0
Recoveries									439	5,331
Net (Charge-offs)/Recoveries									439	5,331
Balance at end of year	49,205				33,602				49,205	33,602	33,487
Reserve for impaired loans	5,254				473				5,254	473
Reserve for non-impaired loans	43,951				33,129				43,951	33,129
Reserve for off-balance sheet credit commitments	101				193				101	193
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Balance at beginning of year				13,108				14,282	13,108	14,282
Provision/(reversal) for loan losses									4,525	(1,906)
Charge-offs									0	0
Recoveries									104	732
Net (Charge-offs)/Recoveries									104	732
Balance at end of year	17,737				13,108				17,737	13,108	14,282
Reserve for impaired loans	145				220				145	220
Reserve for non-impaired loans	17,592				12,888				17,592	12,888
Reserve for off-balance sheet credit commitments	284				311				284	311
Installment and Other Loans [Member ]
Balance at beginning of year				$ 19				$ 18	19	18
Provision/(reversal) for loan losses									(19)	1
Charge-offs									0	0
Recoveries									0	0
Net (Charge-offs)/Recoveries									0	0
Balance at end of year	0				19				0	19	$ 18
Reserve for impaired loans	0				0				0	0
Reserve for non-impaired loans	0				19				0	19
Reserve for off-balance sheet credit commitments	$ 3				$ 3				$ 3	$ 3