Note 4 - Loan Receivables and Allowance for Loan and Lease Losses - Impaired Loans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Impaired loans, related allowance	$ 1,400,000	$ 1,500,000
Impaired loans, recorded investment	24,400,000	19,600,000
With no allowance recorded, average recorded investment	12,783,000	19,123,000	$ 9,563,000
With no allowance recorded, interest income recognized	193,000	279,000	645,000
With allowance recorded, average recorded investment	8,934,000	3,572,000	609,000
With allowance recorded, interest income recognized	42,000	415,000
Impaired Loans, Average recorded investment	21,717,000	22,695,000	10,172,000
Impaired Loans, interest income recognized	235,000	694,000	645,000
Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	15,453,000	10,828,000
Impaired loans with no related allowance recorded, unpaid principal balance	16,692,000	10,992,000
Impaired loans with a related allowance recorded, recorded investment	8,930,000	8,800,000
Impaired loans with a related allowance recorded, unpaid principal balance	8,930,000	8,800,000
Impaired loans, related allowance	1,412,000	1,496,000
Impaired loans, recorded investment	24,383,000	19,628,000
Impaired loans, unpaid principal balance	25,622,000	19,792,000
Commercial Real Estate Portfolio Segment [Member]
With no allowance recorded, average recorded investment	5,859,000	9,829,000	3,318,000
With no allowance recorded, interest income recognized	39,000	95,000	100,000
With allowance recorded, average recorded investment	8,861,000	888,000
With allowance recorded, interest income recognized	35,000	415,000
Impaired Loans, Average recorded investment	14,720,000	10,717,000	3,318,000
Impaired Loans, interest income recognized	74,000	510,000	100,000
Commercial Real Estate Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	5,723,000	4,234,000
Impaired loans with no related allowance recorded, unpaid principal balance	6,644,000	4,309,000
Impaired loans with a related allowance recorded, recorded investment	8,811,000	8,800,000
Impaired loans with a related allowance recorded, unpaid principal balance	8,811,000	8,800,000
Impaired loans, related allowance	1,398,000	1,496,000
Impaired loans, recorded investment	14,534,000	13,034,000
Impaired loans, unpaid principal balance	15,455,000	13,109,000
Residential Portfolio Segment [Member]
With no allowance recorded, average recorded investment	3,681,000	2,531,000	3,154,000
With no allowance recorded, interest income recognized	28,000	104,000	11,000
With allowance recorded, average recorded investment	34,000	952,000	126,000
With allowance recorded, interest income recognized	7,000
Impaired Loans, Average recorded investment	3,715,000	3,483,000	3,280,000
Impaired Loans, interest income recognized	35,000	104,000	11,000
Residential Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	3,853,000	3,621,000
Impaired loans with no related allowance recorded, unpaid principal balance	3,900,000	3,623,000
Impaired loans with a related allowance recorded, recorded investment	109,000
Impaired loans with a related allowance recorded, unpaid principal balance	109,000
Impaired loans, related allowance	4,000
Impaired loans, recorded investment	3,962,000	3,621,000
Impaired loans, unpaid principal balance	4,009,000	3,623,000
Commercial Portfolio Segment [Member]
With no allowance recorded, average recorded investment	2,111,000	1,800,000	987,000
With no allowance recorded, interest income recognized	79,000	45,000
With allowance recorded, average recorded investment		1,714,000	474,000
With allowance recorded, interest income recognized
Impaired Loans, Average recorded investment	2,111,000	3,514,000	1,461,000
Impaired Loans, interest income recognized	79,000	45,000
Commercial Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	4,700,000	2,057,000
Impaired loans with no related allowance recorded, unpaid principal balance	4,816,000	2,060,000
Impaired loans, related allowance
Impaired loans, recorded investment	4,700,000	2,057,000
Impaired loans, unpaid principal balance	4,816,000	2,060,000
Consumer Portfolio Segment [Member]
With no allowance recorded, average recorded investment	1,132,000	901,000	750,000
With no allowance recorded, interest income recognized	47,000	35,000	31,000
With allowance recorded, average recorded investment	39,000	18,000	9,000
With allowance recorded, interest income recognized
Impaired Loans, Average recorded investment	1,171,000	919,000	759,000
Impaired Loans, interest income recognized	47,000	35,000	31,000
Consumer Portfolio Segment [Member] | Business Activities Loans [Member]
Impaired loans with no related allowance recorded, recorded investment	1,177,000	916,000
Impaired loans with no related allowance recorded, unpaid principal balance	1,332,000	1,000,000
Impaired loans with a related allowance recorded, recorded investment	10,000
Impaired loans with a related allowance recorded, unpaid principal balance	10,000
Impaired loans, related allowance	10,000
Impaired loans, recorded investment	1,187,000	916,000
Impaired loans, unpaid principal balance	1,342,000	1,000,000
Construction Portfolio Segment [Member]
With no allowance recorded, average recorded investment		4,062,000	1,354,000
With no allowance recorded, interest income recognized			503,000
Impaired Loans, Average recorded investment		4,062,000	1,354,000
Impaired Loans, interest income recognized			$ 503,000