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, 2021		Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020	Dec. 31, 2020	[1]
Beginning balance	$ 35,913,000		$ 32,246,000	$ 37,967,000		$ 23,889,000
Provision for loan losses	1,900,000		3,200,000	(900,000)		11,550,000
Charge-offs	(743,000)		(123,000)	(865,000)		(499,000)
Recoveries	353,000		249,000	1,221,000		632,000
Ending balance	37,423,000		35,572,000	37,423,000		35,572,000
Ending balance: individually evaluated for impairment	765,000		910,000	765,000		910,000
Ending balance: collectively evaluated for impairment	36,658,000		34,662,000	36,658,000		34,662,000
Ending balance	3,198,056,000			3,198,056,000			$ 2,828,211,000
Ending balance: individually evaluated for impairment	23,409,000			23,409,000			26,958,000
Ending balance: collectively evaluated for impairment	3,174,647,000			3,174,647,000			2,801,253,000
Commercial Portfolio Segment [Member]
Beginning balance	32,092,000		27,962,000	33,779,000		21,070,000
Provision for loan losses	1,859,000		3,499,000	(271,000)		10,539,000
Charge-offs	(690,000)		(45,000)	(771,000)		(360,000)
Recoveries	221,000		194,000	745,000		361,000
Ending balance	33,482,000		31,610,000	33,482,000		31,610,000
Ending balance: individually evaluated for impairment	544,000		480,000	544,000		480,000
Ending balance: collectively evaluated for impairment	32,938,000		31,130,000	32,938,000		31,130,000
Ending balance	2,726,706,000	[2]		2,726,706,000	[2]		2,428,703,000
Ending balance: individually evaluated for impairment	19,337,000	[2]		19,337,000	[2]		22,415,000
Ending balance: collectively evaluated for impairment	2,707,369,000	[2]		2,707,369,000	[2]		2,406,288,000
Retail Portfolio Segment [Member]
Beginning balance	3,636,000		4,224,000	4,129,000		2,749,000
Provision for loan losses	41,000		(266,000)	(755,000)		1,054,000
Charge-offs	(53,000)		(78,000)	(94,000)		(139,000)
Recoveries	132,000		55,000	476,000		271,000
Ending balance	3,756,000		3,935,000	3,756,000		3,935,000
Ending balance: individually evaluated for impairment	221,000		430,000	221,000		430,000
Ending balance: collectively evaluated for impairment	3,535,000		3,505,000	3,535,000		3,505,000
Ending balance	471,350,000			471,350,000			399,508,000
Ending balance: individually evaluated for impairment	4,072,000			4,072,000			4,543,000
Ending balance: collectively evaluated for impairment	467,278,000			467,278,000			$ 394,965,000
Unallocated Financing Receivables [Member]
Beginning balance	185,000		60,000	59,000		70,000
Provision for loan losses	0		(33,000)	126,000		(43,000)
Charge-offs	0		0	0		0
Recoveries	0		0	0		0
Ending balance	185,000		27,000	185,000		27,000
Ending balance: individually evaluated for impairment	0		0	0		0
Ending balance: collectively evaluated for impairment	$ 185,000		$ 27,000	$ 185,000		$ 27,000

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

[2] Excludes $116 million in loans originated under the Paycheck Protection Program.