Note 4 - Loans Receivable and Related Allowance for Loan Losses - Impaired Loans by Class (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Impaired loans with specific allowance, unpaid principal balance	$ 69	$ 76	$ 69	$ 76	$ 76
Impaired loans with specific allowance, recorded investment	69	76	69	76	76
Related allowance	15	4	15	4	5
Impaired loans with specific allowance, average recorded investment	107	77	140	94	77
Impaired loans with specific allowance, interest income recognized in period	1	1	2	3	3
Impaired loans with specific allowance, cash basis interest recognized in period	1	1	2	3	3
Impaired loans with no specific allowance, unpaid principal balance	2,147	2,880	2,147	2,880	519
Impaired loans with no specific allowance, recorded investment	2,036	2,805	2,036	2,805	407
Impaired loans with no specific allowance, average recorded investment	2,147	2,912	1,522	1,648	1,399
Impaired loans with no specific allowance, interest income recognized in period	30	36	89	97	99
Impaired loans with no specific allowance, cash basis interest recognized in period	28	35	70	39	41
Residential Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance		72		72	72
Impaired loans with specific allowance, recorded investment		72		72	72
Related allowance		4		4	5
Impaired loans with specific allowance, average recorded investment	35	72	53	73	72
Impaired loans with specific allowance, interest income recognized in period		1		3	3
Impaired loans with specific allowance, cash basis interest recognized in period		1		3	3
Impaired loans with no specific allowance, unpaid principal balance	336	369	336	369	398
Impaired loans with no specific allowance, recorded investment	225	294	225	294	286
Impaired loans with no specific allowance, average recorded investment	304	298	293	305	301
Impaired loans with no specific allowance, interest income recognized in period	3	2	6	3	4
Impaired loans with no specific allowance, cash basis interest recognized in period	3	2	6	3	4
Home Equity Loans and Lines of Credit [Member]
Impaired loans with specific allowance, unpaid principal balance		4		4	4
Impaired loans with specific allowance, recorded investment		4		4	4
Related allowance
Impaired loans with specific allowance, average recorded investment	2	5	3	5	5
Impaired loans with specific allowance, interest income recognized in period
Impaired loans with specific allowance, cash basis interest recognized in period
Impaired loans with no specific allowance, unpaid principal balance	4		4
Impaired loans with no specific allowance, recorded investment	4		4
Impaired loans with no specific allowance, average recorded investment	2		1
Impaired loans with no specific allowance, interest income recognized in period
Impaired loans with no specific allowance, cash basis interest recognized in period
Commercial Real Estate Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance
Impaired loans with specific allowance, recorded investment
Related allowance
Impaired loans with specific allowance, average recorded investment			37
Impaired loans with specific allowance, interest income recognized in period
Impaired loans with specific allowance, cash basis interest recognized in period
Impaired loans with no specific allowance, unpaid principal balance	1,694	2,471	1,694	2,471	81
Impaired loans with no specific allowance, recorded investment	1,694	2,471	1,694	2,471	81
Impaired loans with no specific allowance, average recorded investment	1,714	2,475	1,144	1,254	1,019
Impaired loans with no specific allowance, interest income recognized in period	23	34	75	87	88
Impaired loans with no specific allowance, cash basis interest recognized in period	23	33	59	34	35
Commercial Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance	69		69
Impaired loans with specific allowance, recorded investment	69		69
Related allowance	15		15
Impaired loans with specific allowance, average recorded investment	70		47	16
Impaired loans with specific allowance, interest income recognized in period	1		2
Impaired loans with specific allowance, cash basis interest recognized in period	1		2
Impaired loans with no specific allowance, unpaid principal balance	113	40	113	40	40
Impaired loans with no specific allowance, recorded investment	113	40	113	40	40
Impaired loans with no specific allowance, average recorded investment	127	139	84	89	79
Impaired loans with no specific allowance, interest income recognized in period	4		8	7	7
Impaired loans with no specific allowance, cash basis interest recognized in period	2		5	2	2
Consumer Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance
Impaired loans with specific allowance, recorded investment
Related allowance
Impaired loans with specific allowance, average recorded investment
Impaired loans with specific allowance, interest income recognized in period
Impaired loans with specific allowance, cash basis interest recognized in period
Impaired loans with no specific allowance, unpaid principal balance
Impaired loans with no specific allowance, recorded investment
Impaired loans with no specific allowance, average recorded investment
Impaired loans with no specific allowance, interest income recognized in period
Impaired loans with no specific allowance, cash basis interest recognized in period