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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Beginning balance	$ 32,246,000	$ 24,053,000	$ 23,889,000	$ 22,380,000
Provision for loan losses	3,200,000	700,000	11,550,000	2,450,000
Charge-offs	(123,000)	(519,000)	(499,000)	(771,000)
Recoveries	249,000	180,000	632,000	355,000
Ending balance	35,572,000	24,414,000	35,572,000	24,414,000
Ending balance: individually evaluated for impairment	910,000	2,345,000	910,000	2,345,000
Ending balance: collectively evaluated for impairment	34,662,000	22,069,000	34,662,000	22,069,000
Loans and Leases Receivable, Net of Deferred Income, Total	3,350,544,000		3,350,544,000		$ 2,856,667,000
Ending balance: individually evaluated for impairment	16,105,000		16,105,000		15,056,000
Ending balance: collectively evaluated for impairment	3,334,439,000		3,334,439,000		2,841,611,000
Commercial Portfolio Segment [Member]
Beginning balance	27,962,000	21,271,000	21,070,000	19,619,000
Provision for loan losses	3,499,000	499,000	10,539,000	2,077,000
Charge-offs	(45,000)	(405,000)	(360,000)	(407,000)
Recoveries	194,000	96,000	361,000	172,000
Ending balance	31,610,000	21,461,000	31,610,000	21,461,000
Ending balance: individually evaluated for impairment	480,000	1,792,000	480,000	1,792,000
Ending balance: collectively evaluated for impairment	31,130,000	19,669,000	31,130,000	19,669,000
Loans and Leases Receivable, Net of Deferred Income, Total	2,938,361,000		2,938,361,000		2,441,544,000
Ending balance: individually evaluated for impairment	11,323,000		11,323,000		10,986,000
Ending balance: collectively evaluated for impairment	2,927,038,000		2,927,038,000		2,430,558,000
Retail Portfolio Segment [Member]
Beginning balance	4,224,000	2,685,000	2,749,000	2,717,000
Provision for loan losses	(266,000)	132,000	1,054,000	251,000
Charge-offs	(78,000)	(114,000)	(139,000)	(364,000)
Recoveries	55,000	84,000	271,000	183,000
Ending balance	3,935,000	2,787,000	3,935,000	2,787,000
Ending balance: individually evaluated for impairment	430,000	553,000	430,000	553,000
Ending balance: collectively evaluated for impairment	3,505,000	2,234,000	3,505,000	2,234,000
Loans and Leases Receivable, Net of Deferred Income, Total	412,183,000		412,183,000		415,123,000
Ending balance: individually evaluated for impairment	4,782,000		4,782,000		4,070,000
Ending balance: collectively evaluated for impairment	407,401,000		407,401,000		411,053,000
Unallocated Financing Receivables [Member]
Beginning balance	60,000	97,000	70,000	44,000
Provision for loan losses	(33,000)	69,000	(43,000)	122,000
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Ending balance	27,000	166,000	27,000	166,000
Ending balance: individually evaluated for impairment	0	0	0	0
Ending balance: collectively evaluated for impairment	27,000	$ 166,000	27,000	$ 166,000
Loans and Leases Receivable, Net of Deferred Income, Total
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment