Note 8 - Loans - Allowance for Loan Losses by Portfolio Segment and Based on Impairment Method (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Loans individually evaluated for impairment, allowance	$ 3,451		$ 3,236
Loans individually evaluated for impairment, balance	88,097		75,859
Loans collectively evaluated for impairment, allowance	144,822		119,988
Loans collectively evaluated for impairment, balance	15,446,115		14,999,622
Loans, allowance	148,273		123,224
Loans	15,534,212		15,075,481
Balance	123,224	$ 122,391
Provision/(reversal) for possible credit losses	25,000	0
Charge-offs	(1,321)	(1,231)
Recoveries	1,370	1,395
Net (charge-offs)/recoveries	49	164
Balance	148,273	122,555
Reserve for impaired loans	3,451	1,414
Reserve for non-impaired loans	144,822	121,141
Reserve for off-balance sheet credit commitments	3,013	3,850
Commercial Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	2,827		2,543
Loans individually evaluated for impairment, balance	35,143		24,596
Loans collectively evaluated for impairment, allowance	64,972		54,478
Loans collectively evaluated for impairment, balance	2,937,935		2,754,148
Loans, allowance	67,799		57,021
Loans	2,973,078		2,778,744
Balance	57,021	54,978
Provision/(reversal) for possible credit losses	10,891	962
Charge-offs	(1,321)	(1,231)
Recoveries	1,208	41
Net (charge-offs)/recoveries	(113)	(1,190)
Balance	67,799	54,750
Reserve for impaired loans	2,827	498
Reserve for non-impaired loans	64,972	54,252
Reserve for off-balance sheet credit commitments	1,296	1,759
Real Estate Construction Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	0		0
Loans individually evaluated for impairment, balance	4,482		4,580
Loans collectively evaluated for impairment, allowance	23,222		19,474
Loans collectively evaluated for impairment, balance	572,758		575,284
Loans, allowance	23,222		19,474
Loans	577,240		579,864
Balance	19,474	19,626
Provision/(reversal) for possible credit losses	3,748	53
Charge-offs	0	0
Recoveries	0	1,044
Net (charge-offs)/recoveries	0	1,044
Balance	23,222	20,723
Reserve for impaired loans	0	0
Reserve for non-impaired loans	23,222	20,723
Reserve for off-balance sheet credit commitments	1,233	1,668
Commercial Real Estate Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	405		473
Loans individually evaluated for impairment, balance	36,643		35,070
Loans collectively evaluated for impairment, allowance	39,481		33,129
Loans collectively evaluated for impairment, balance	7,385,942		7,240,192
Loans, allowance	39,886		33,602
Loans	7,422,585		7,275,262
Balance	33,602	33,487
Provision/(reversal) for possible credit losses	6,129	(566)
Charge-offs	0	0
Recoveries	155	152
Net (charge-offs)/recoveries	155	152
Balance	39,886	33,073
Reserve for impaired loans	405	667
Reserve for non-impaired loans	39,481	32,406
Reserve for off-balance sheet credit commitments	177	146
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	219		220
Loans individually evaluated for impairment, balance	11,829		11,613
Loans collectively evaluated for impairment, allowance	17,147		12,888
Loans collectively evaluated for impairment, balance	4,547,364		4,424,948
Loans, allowance	17,366		13,108
Loans	4,559,193		4,436,561
Balance	13,108	14,282
Provision/(reversal) for possible credit losses	4,251	(465)
Charge-offs	0	0
Recoveries	7	158
Net (charge-offs)/recoveries	7	158
Balance	17,366	13,975
Reserve for impaired loans	219	249
Reserve for non-impaired loans	17,147	13,726
Reserve for off-balance sheet credit commitments	304	275
Installment and Other Loans [Member ]
Loans individually evaluated for impairment, allowance	0
Loans individually evaluated for impairment, balance	0
Loans collectively evaluated for impairment, allowance	0
Loans collectively evaluated for impairment, balance	2,116
Loans, allowance	0
Loans	2,116		5,050
Balance	19	18
Provision/(reversal) for possible credit losses	(19)	16
Charge-offs	0	0
Recoveries	0	0
Net (charge-offs)/recoveries	0	0
Balance	0	34
Reserve for impaired loans	0	0
Reserve for non-impaired loans	0	34
Reserve for off-balance sheet credit commitments	3	$ 2
Consumer Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance			0
Loans individually evaluated for impairment, balance			0
Loans collectively evaluated for impairment, allowance			19
Loans collectively evaluated for impairment, balance			5,050
Loans, allowance			19
Loans	$ 2,116		$ 5,050

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

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of increase in allowance for credit loss on financing receivable from recovery.

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The balance of financing receivables that were collectively evaluated for impairment.

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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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