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
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Provision for loan losses	$ 850,000	$ 0
Loans and Leases Receivable, Net of Deferred Income, Total	2,799,639,000		$ 2,753,085,000
Originated Loan [Member]
Beginning balance	21,554,000	19,133,000
Provision for loan losses	969,000	(782,000)
Charge-offs	(174,000)	(393,000)
Recoveries	69,000	1,123,000
Ending balance	22,418,000	19,081,000
Ending balance: individually evaluated for impairment	1,046,000	863,000
Ending balance: collectively evaluated for impairment	21,372,000	18,218,000
Loans and Leases Receivable, Net of Deferred Income, Total	2,511,036,000		2,452,446,000
Ending balance: individually evaluated for impairment	20,191,000		18,882,000
Ending balance: collectively evaluated for impairment	2,490,845,000		2,433,564,000
Acquired Loan [Member]
Beginning balance	826,000	368,000
Provision for loan losses	(119,000)	782,000
Charge-offs	0	(261,000)
Recoveries	10,000	4,000
Ending balance	717,000	893,000
Loans and Leases Receivable, Net of Deferred Income, Total	288,603,000		300,639,000
Commercial Portfolio Segment [Member]
Loans and Leases Receivable, Net of Deferred Income, Total	2,400,198,000		2,360,106,000
Commercial Portfolio Segment [Member] | Originated Loan [Member]
Beginning balance	19,442,000	16,456,000
Provision for loan losses	578,000	(341,000)
Charge-offs	0	(258,000)
Recoveries	30,000	1,008,000
Ending balance	20,050,000	16,865,000
Ending balance: individually evaluated for impairment	855,000	547,000
Ending balance: collectively evaluated for impairment	19,195,000	16,318,000
Loans and Leases Receivable, Net of Deferred Income, Total	2,198,713,000		2,151,998,000
Ending balance: individually evaluated for impairment	18,503,000		17,134,000
Ending balance: collectively evaluated for impairment	2,180,210,000		2,134,864,000
Commercial Portfolio Segment [Member] | Acquired Loan [Member]
Beginning balance	177,000	291,000
Provision for loan losses	(16,000)	314,000
Charge-offs	0	(246,000)
Recoveries	0	0
Ending balance	161,000	359,000
Loans and Leases Receivable, Net of Deferred Income, Total	201,485,000		208,108,000
Retail Portfolio Segment [Member]
Loans and Leases Receivable, Net of Deferred Income, Total	399,441,000		392,979,000
Retail Portfolio Segment [Member] | Originated Loan [Member]
Beginning balance	2,068,000	2,584,000
Provision for loan losses	207,000	(563,000)
Charge-offs	(174,000)	(135,000)
Recoveries	39,000	115,000
Ending balance	2,140,000	2,001,000
Ending balance: individually evaluated for impairment	191,000	316,000
Ending balance: collectively evaluated for impairment	1,949,000	1,685,000
Loans and Leases Receivable, Net of Deferred Income, Total	312,323,000		300,448,000
Ending balance: individually evaluated for impairment	1,688,000		1,748,000
Ending balance: collectively evaluated for impairment	310,635,000		298,700,000
Retail Portfolio Segment [Member] | Acquired Loan [Member]
Beginning balance	649,000	77,000
Provision for loan losses	(103,000)	468,000
Charge-offs	0	(15,000)
Recoveries	10,000	4,000
Ending balance	556,000	534,000
Loans and Leases Receivable, Net of Deferred Income, Total	87,118,000		$ 92,531,000
Unallocated Financing Receivables [Member] | Originated Loan [Member]
Beginning balance	44,000	93,000
Provision for loan losses	184,000	122,000
Charge-offs	0	0
Recoveries	0	0
Ending balance	228,000	215,000
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	228,000	215,000
Unallocated Financing Receivables [Member] | Acquired Loan [Member]
Beginning balance	0	0
Provision for loan losses	0	0
Charge-offs	0	0
Recoveries	0	0
Ending balance	$ 0	$ 0