Note 4 - Loans Receivable and Related Allowance for Loan Losses - Impaired Loans by Class (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Impaired loans with specific allowance, unpaid principal balance	$ 506	$ 270	$ 458
Impaired loans with specific allowance, recorded investment	506	270	458
Related allowance	40	26	60
Impaired loans with specific allowance, average recorded investment	482	173	204
Impaired loans with specific allowance, interest income recognized in period	6	2	22
Impaired loans with specific allowance, cash basis interest recognized in period	6	2	15
Impaired loans with no specific allowance, unpaid principal balance	1,542	1,500	1,767
Impaired loans with no specific allowance, recorded investment	1,414	1,388	1,656
Impaired loans with no specific allowance, average recorded investment	1,536	897	1,549
Impaired loans with no specific allowance, interest income recognized in period	14	15	93
Impaired loans with no specific allowance, cash basis interest recognized in period	14	14	79
Residential Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance	69	71
Impaired loans with specific allowance, recorded investment	69	71
Related allowance	1	2
Impaired loans with specific allowance, average recorded investment	35	71	43
Impaired loans with specific allowance, interest income recognized in period	1	1
Impaired loans with specific allowance, cash basis interest recognized in period	1	1
Impaired loans with no specific allowance, unpaid principal balance	363	390	440
Impaired loans with no specific allowance, recorded investment	251	278	329
Impaired loans with no specific allowance, average recorded investment	290	282	300
Impaired loans with no specific allowance, interest income recognized in period	1	1	7
Impaired loans with no specific allowance, cash basis interest recognized in period	1	1	7
Home Equity Loans and Lines of Credit [Member]
Impaired loans with specific allowance, unpaid principal balance		4
Impaired loans with specific allowance, recorded investment		4
Related allowance
Impaired loans with specific allowance, average recorded investment		4	2
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		3
Impaired loans with no specific allowance, recorded investment	4		3
Impaired loans with no specific allowance, average recorded investment	4		2
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	373	150	380
Impaired loans with specific allowance, recorded investment	373	150	380
Related allowance	33	19	40
Impaired loans with specific allowance, average recorded investment	376	75	106
Impaired loans with specific allowance, interest income recognized in period	4		17
Impaired loans with specific allowance, cash basis interest recognized in period	4		11
Impaired loans with no specific allowance, unpaid principal balance	1,110	1,067	1,259
Impaired loans with no specific allowance, recorded investment	1,094	1,067	1,259
Impaired loans with no specific allowance, average recorded investment	1,177	574	1,167
Impaired loans with no specific allowance, interest income recognized in period	12	13	76
Impaired loans with no specific allowance, cash basis interest recognized in period	12	13	66
Commercial Portfolio Segment [Member]
Impaired loans with specific allowance, unpaid principal balance	64	45	78
Impaired loans with specific allowance, recorded investment	64	45	78
Related allowance	6	5	20
Impaired loans with specific allowance, average recorded investment	71	23	53
Impaired loans with specific allowance, interest income recognized in period	1	1	5
Impaired loans with specific allowance, cash basis interest recognized in period	1	1	4
Impaired loans with no specific allowance, unpaid principal balance	65	43	65
Impaired loans with no specific allowance, recorded investment	65	43	65
Impaired loans with no specific allowance, average recorded investment	65	41	80
Impaired loans with no specific allowance, interest income recognized in period	1	1	10
Impaired loans with no specific allowance, cash basis interest recognized in period	1		6
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

Amount of allowance for credit losses related to recorded investment.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5258-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

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- Definition

Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524

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- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

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- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5258-111524

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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Amount of interest income on financing receivables, for which there is a related allowance for credit losses, recognized on a cash-basis method of accounting that the financing receivables were impaired.

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Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

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- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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