Note 3 - Loans and Allowance for Loan Losses - Activity in Allowance for Loan Losses and the Recorded Investments in Loans (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Provision for loan losses	$ 700,000	$ 400,000	$ 2,450,000	$ 1,100,000
Loans and Leases Receivable, Net of Deferred Income, Total	2,933,013,000		2,933,013,000		$ 2,753,085,000
Originated Loan [Member]
Beginning balance	23,331,000	20,482,000	21,554,000	19,133,000
Provision for loan losses	740,000	473,000	2,607,000	605,000
Charge-offs	(519,000)	(169,000)	(771,000)	(835,000)
Recoveries	180,000	290,000	342,000	2,173,000
Ending balance	23,732,000	21,076,000	23,732,000	21,076,000
Ending balance: individually evaluated for impairment	2,025,000	998,000	2,025,000	998,000
Ending balance: collectively evaluated for impairment	21,707,000	20,078,000	21,707,000	20,078,000
Loans and Leases Receivable, Net of Deferred Income, Total	2,690,177,000		2,690,177,000		2,452,446,000
Ending balance: individually evaluated for impairment	27,662,000		27,662,000		18,882,000
Ending balance: collectively evaluated for impairment	2,662,515,000		2,662,515,000		2,433,564,000
Acquired Loan [Member]
Beginning balance	722,000	685,000	826,000	368,000
Provision for loan losses	(40,000)	(73,000)	(157,000)	495,000
Charge-offs	0	0	0	(261,000)
Recoveries	0	4,000	13,000	14,000
Ending balance	682,000	616,000	682,000	616,000
Loans and Leases Receivable, Net of Deferred Income, Total	242,836,000		242,836,000		300,639,000
Commercial Portfolio Segment [Member]
Loans and Leases Receivable, Net of Deferred Income, Total	2,508,367,000		2,508,367,000		2,360,106,000
Commercial Portfolio Segment [Member] | Originated Loan [Member]
Beginning balance	21,073,000	18,326,000	19,442,000	16,456,000
Provision for loan losses	522,000	371,000	2,080,000	922,000
Charge-offs	(405,000)	0	(407,000)	(342,000)
Recoveries	96,000	63,000	171,000	1,724,000
Ending balance	21,286,000	18,760,000	21,286,000	18,760,000
Ending balance: individually evaluated for impairment	1,699,000	750,000	1,699,000	750,000
Ending balance: collectively evaluated for impairment	19,587,000	18,010,000	19,587,000	18,010,000
Loans and Leases Receivable, Net of Deferred Income, Total	2,341,797,000		2,341,797,000		2,151,998,000
Ending balance: individually evaluated for impairment	25,898,000		25,898,000		17,134,000
Ending balance: collectively evaluated for impairment	2,315,899,000		2,315,899,000		2,134,864,000
Commercial Portfolio Segment [Member] | Acquired Loan [Member]
Beginning balance	198,000	105,000	177,000	291,000
Provision for loan losses	(23,000)	9,000	(3,000)	69,000
Charge-offs	0	0	0	(246,000)
Recoveries	0	0	1,000	0
Ending balance	175,000	114,000	175,000	114,000
Loans and Leases Receivable, Net of Deferred Income, Total	166,570,000		166,570,000		208,108,000
Retail Portfolio Segment [Member]
Loans and Leases Receivable, Net of Deferred Income, Total	424,646,000		424,646,000		392,979,000
Retail Portfolio Segment [Member] | Originated Loan [Member]
Beginning balance	2,161,000	2,216,000	2,068,000	2,584,000
Provision for loan losses	149,000	(41,000)	405,000	(307,000)
Charge-offs	(114,000)	(169,000)	(364,000)	(493,000)
Recoveries	84,000	227,000	171,000	449,000
Ending balance	2,280,000	2,233,000	2,280,000	2,233,000
Ending balance: individually evaluated for impairment	326,000	248,000	326,000	248,000
Ending balance: collectively evaluated for impairment	1,954,000	1,985,000	1,954,000	1,985,000
Loans and Leases Receivable, Net of Deferred Income, Total	348,380,000		348,380,000		300,448,000
Ending balance: individually evaluated for impairment	1,764,000		1,764,000		1,748,000
Ending balance: collectively evaluated for impairment	346,616,000		346,616,000		298,700,000
Retail Portfolio Segment [Member] | Acquired Loan [Member]
Beginning balance	524,000	580,000	649,000	77,000
Provision for loan losses	(17,000)	(82,000)	(154,000)	426,000
Charge-offs	0	0	0	(15,000)
Recoveries	0	4,000	12,000	14,000
Ending balance	507,000	502,000	507,000	502,000
Loans and Leases Receivable, Net of Deferred Income, Total	76,266,000		76,266,000		92,531,000
Unallocated Financing Receivables [Member] | Originated Loan [Member]
Beginning balance	97,000	(60,000)	44,000	93,000
Provision for loan losses	69,000	143,000	122,000	(10,000)
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	166,000	83,000	166,000	83,000
Ending balance: individually evaluated for impairment	0	0	0	0
Ending balance: collectively evaluated for impairment	166,000	83,000	166,000	83,000
Loans and Leases Receivable, Net of Deferred Income, Total
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment
Unallocated Financing Receivables [Member] | Acquired Loan [Member]
Beginning balance	0	0	0	0
Provision for loan losses	0	0	0	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0