Note 8 - Loans - Allowance for Loan Losses by Portfolio Segment and Based on Impairment Method (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Loans individually evaluated for impairment, allowance	$ 1,502		$ 2,134
Loans individually evaluated for impairment, balance	132,113		117,353
Loans collectively evaluated for impairment, allowance	120,582		121,145
Loans collectively evaluated for impairment, balance	12,882,426		12,752,937
Loans, allowance	122,084		123,279
Loans	13,014,539		12,870,290
Beginning Balance	123,279	$ 118,966
Provision/(credit) for possible credit losses	(3,000)	(2,500)
Charge-offs	(19)	(1,759)
Recoveries	1,824	837
Net recoveries	1,805	(922)
Ending Balance	122,084	115,544
Reserve for impaired loans	1,502	2,275
Reserve for non-impaired loans	120,582	113,269
Reserve for off-balance sheet credit commitments	4,588	3,424
Commercial Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	11		43
Loans individually evaluated for impairment, balance	44,911		43,495
Loans collectively evaluated for impairment, allowance	54,586		49,753
Loans collectively evaluated for impairment, balance	2,391,510		2,417,771
Loans, allowance	54,597		49,796
Loans	2,436,421		2,461,266
Beginning Balance	49,796	49,203
Provision/(credit) for possible credit losses	3,907	(1,214)
Charge-offs	(19)	(1,204)
Recoveries	913	491
Net recoveries	894	(713)
Ending Balance	54,597	47,276
Reserve for impaired loans	11	1,062
Reserve for non-impaired loans	54,586	46,214
Reserve for off-balance sheet credit commitments	2,747	2,243
Real Estate Construction Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance
Loans individually evaluated for impairment, balance	8,113		8,185
Loans collectively evaluated for impairment, allowance	21,864		24,838
Loans collectively evaluated for impairment, balance	579,814		670,620
Loans, allowance	21,864		24,838
Loans	587,927		678,805
Beginning Balance	24,838	23,268
Provision/(credit) for possible credit losses	(3,018)	(3,549)
Charge-offs
Recoveries	44	49
Net recoveries	44	49
Ending Balance	21,864	19,768
Reserve for impaired loans
Reserve for non-impaired loans	21,864	19,768
Reserve for off-balance sheet credit commitments	1,515	909
Commercial Real Estate Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	1,145		1,738
Loans individually evaluated for impairment, balance	64,747		52,664
Loans collectively evaluated for impairment, allowance	33,085		35,872
Loans collectively evaluated for impairment, balance	6,545,507		6,430,031
Loans, allowance	34,230		37,610
Loans	6,610,254		6,482,695
Beginning Balance	37,610	34,864
Provision/(credit) for possible credit losses	(4,163)	1,362
Charge-offs		(555)
Recoveries	783	289
Net recoveries	783	(266)
Ending Balance	34,230	35,960
Reserve for impaired loans	1,145	818
Reserve for non-impaired loans	33,085	35,142
Reserve for off-balance sheet credit commitments	138	120
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	346		353
Loans individually evaluated for impairment, balance	14,342		13,009
Loans collectively evaluated for impairment, allowance	11,026		10,660
Loans collectively evaluated for impairment, balance	3,361,122		3,229,345
Loans, allowance	11,372		11,013
Loans	3,375,464		3,242,354
Beginning Balance	11,013	11,620
Provision/(credit) for possible credit losses	275	898
Charge-offs
Recoveries	84	8
Net recoveries	84	8
Ending Balance	11,372	12,526
Reserve for impaired loans	346	395
Reserve for non-impaired loans	11,026	12,131
Reserve for off-balance sheet credit commitments	182	146
Installment and Other Loans [Member ]
Loans	4,473		5,170
Beginning Balance	22	11
Provision/(credit) for possible credit losses	(1)	3
Charge-offs
Recoveries
Net recoveries
Ending Balance	21	14
Reserve for impaired loans
Reserve for non-impaired loans	21	14
Reserve for off-balance sheet credit commitments	6	$ 6
Consumer Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance
Loans individually evaluated for impairment, balance
Loans collectively evaluated for impairment, allowance	21		22
Loans collectively evaluated for impairment, balance	4,473		5,170
Loans, allowance	21		22
Loans	$ 4,473		$ 5,170

Financing Receivable, Allowance For Credit Losses, Net Charge-Offs

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Amount of provision (reversal) related to loan transactions based on the assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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