Note 5 - Loans - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance at beginning of year				$ 118,966				$ 138,963	$ 118,966	$ 138,963	$ 161,420
Provision/(reversal) for loan losses				(2,500)			$ (5,150)	(10,500)	(2,500)	(15,650)	(11,400)
Charge-offs									(4,173)	(18,903)	(20,427)
Recoveries									10,986	14,556	9,370
Net (Charge-offs)/Recoveries									6,813	(4,347)
Balance at end of year	123,279				118,966				123,279	118,966	138,963
Reserve for impaired loans	2,134				2,796				2,134	2,796
Reserve for non-impaired loans	121,145				116,170				121,145	116,170
Reserve for off-balance sheet credit commitments	4,588				3,224				4,588	3,224
Commercial Portfolio Segment [Member]
Balance at beginning of year				49,203				56,199	49,203	56,199
Provision/(reversal) for loan losses									117	1,815
Charge-offs									(3,313)	(12,955)
Recoveries									3,402	4,144
Net (Charge-offs)/Recoveries									89	(8,811)
Balance at end of year	49,796				49,203				49,796	49,203	56,199
Reserve for impaired loans	43				1,827				43	1,827
Reserve for non-impaired loans	49,753				47,376				49,753	47,376
Reserve for off-balance sheet credit commitments	2,919				2,091				2,919	2,091
Real Estate Construction Portfolio Segment [Member]
Balance at beginning of year				23,268				22,170	23,268	22,170
Provision/(reversal) for loan losses									955	(6,819)
Charge-offs
Recoveries									229	7,917
Net (Charge-offs)/Recoveries									229	7,917
Balance at end of year	24,838				23,268				24,838	23,268	22,170
Reserve for impaired loans
Reserve for non-impaired loans	24,838				23,268				24,838	23,268
Reserve for off-balance sheet credit commitments	1,360				940				1,360	940
Commercial Real Estate Portfolio Segment [Member]
Balance at beginning of year				34,864				49,440	34,864	49,440
Provision/(reversal) for loan losses									(2,778)	(11,123)
Charge-offs									(860)	(5,948)
Recoveries									7,329	2,495
Net (Charge-offs)/Recoveries									6,469	(3,453)
Balance at end of year	37,610				34,864				37,610	34,864	49,440
Reserve for impaired loans	1,738				573				1,738	573
Reserve for non-impaired loans	35,872				34,291				35,872	34,291
Reserve for off-balance sheet credit commitments	114				41				114	41
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Balance at beginning of year				11,620				11,145	11,620	11,145
Provision/(reversal) for loan losses									(798)	475
Charge-offs
Recoveries									19
Net (Charge-offs)/Recoveries									19
Balance at end of year	11,013				11,620				11,013	11,620	11,145
Reserve for impaired loans	353				396				353	396
Reserve for non-impaired loans	10,660				11,224				10,660	11,224
Reserve for off-balance sheet credit commitments	190				146				190	146
Installment and Other Loans [Member ]
Balance at beginning of year				$ 11				$ 9	11	9
Provision/(reversal) for loan losses									4	2
Charge-offs
Recoveries									7
Net (Charge-offs)/Recoveries									7
Balance at end of year	22				11				22	11	$ 9
Reserve for impaired loans
Reserve for non-impaired loans	22				11				22	11
Reserve for off-balance sheet credit commitments	$ 5				$ 6				$ 5	$ 6