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			6 Months Ended
	Jun. 30, 2021		Jun. 30, 2020	Jun. 30, 2021		Jun. 30, 2020	Dec. 31, 2020	[2]
Beginning balance	$ 38,695,000		$ 24,828,000	$ 37,967,000		$ 23,889,000
Provision for loan losses	(3,100,000)		7,600,000	(2,800,000)		8,350,000
Charge-offs	(68,000)		(335,000)	(121,000)		(375,000)
Recoveries	386,000		153,000	867,000		382,000
Ending balance	35,913,000		32,246,000	35,913,000		32,246,000
Ending balance: individually evaluated for impairment	787,000		1,512,000	787,000		1,512,000
Ending balance: collectively evaluated for impairment	35,126,000		30,734,000	35,126,000		30,734,000
Ending balance	3,003,058,000	[1]		3,003,058,000	[1]		$ 2,828,211,000
Ending balance: individually evaluated for impairment	23,915,000			23,915,000			26,958,000
Ending balance: collectively evaluated for impairment	2,979,143,000			2,979,143,000			2,801,253,000
Commercial Portfolio Segment [Member]
Beginning balance	34,711,000		21,750,000	33,779,000		21,070,000
Provision for loan losses	(2,712,000)		6,466,000	(2,130,000)		7,039,000
Charge-offs	(66,000)		(301,000)	(81,000)		(314,000)
Recoveries	159,000		47,000	524,000		167,000
Ending balance	32,092,000		27,962,000	32,092,000		27,962,000
Ending balance: individually evaluated for impairment	477,000		1,011,000	477,000		1,011,000
Ending balance: collectively evaluated for impairment	31,615,000		26,951,000	31,615,000		26,951,000
Ending balance	2,564,526,000	[1]		2,564,526,000	[1]		2,428,703,000
Ending balance: individually evaluated for impairment	19,691,000	[1]		19,691,000	[1]		22,415,000
Ending balance: collectively evaluated for impairment	2,544,835,000	[1]		2,544,835,000	[1]		2,406,288,000
Retail Portfolio Segment [Member]
Beginning balance	3,794,000		3,078,000	4,129,000		2,749,000
Provision for loan losses	(383,000)		1,074,000	(796,000)		1,321,000
Charge-offs	(2,000)		(34,000)	(40,000)		(61,000)
Recoveries	227,000		106,000	343,000		215,000
Ending balance	3,636,000		4,224,000	3,636,000		4,224,000
Ending balance: individually evaluated for impairment	310,000		501,000	310,000		501,000
Ending balance: collectively evaluated for impairment	3,326,000		3,723,000	3,326,000		3,723,000
Ending balance	438,532,000	[1]		438,532,000	[1]		399,508,000
Ending balance: individually evaluated for impairment	4,224,000			4,224,000			4,543,000
Ending balance: collectively evaluated for impairment	434,308,000			434,308,000			$ 394,965,000
Unallocated Financing Receivables [Member]
Beginning balance	190,000		0	59,000		70,000
Provision for loan losses	(5,000)		60,000	126,000		(10,000)
Charge-offs	0		0	0		0
Recoveries	0		0	0		0
Ending balance	185,000		60,000	185,000		60,000
Ending balance: individually evaluated for impairment	0		0	0		0
Ending balance: collectively evaluated for impairment	$ 185,000		$ 60,000	$ 185,000		$ 60,000

[1] Excludes $246 million in loans originated under the Paycheck Protection Program.

[2] Excludes $365 million in loans originated under the Paycheck Protection Program.