Note 6 - Loans Receivable, Net and Allowance for Loan Losses - Troubled Debt Restructuring Loans (Details)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Troubled debt restructuring, number of contracts	2	2
Troubled debt restructuring, recorded investment	$ 140,000	$ 140,000
Troubled debt restructuring, related allowance	0	0
Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	9,000	9,000
Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 131,000	$ 131,000
Real Estate Portfolio Segment [Member] | One-to-four Family Residential Owner Occupied Loans [Member]
Troubled debt restructuring, number of contracts	0	0
Troubled debt restructuring, recorded investment	$ 0	$ 0
Troubled debt restructuring, related allowance	0	0
Real Estate Portfolio Segment [Member] | One-to-four Family Residential Owner Occupied Loans [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	0	0
Real Estate Portfolio Segment [Member] | One-to-four Family Residential Owner Occupied Loans [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 0	$ 0
Real Estate Portfolio Segment [Member] | One-to-four Family Residential Non-owner Occupied Loans [Member]
Troubled debt restructuring, number of contracts	1	1
Troubled debt restructuring, recorded investment	$ 9,000	$ 9,000
Troubled debt restructuring, related allowance	0	0
Real Estate Portfolio Segment [Member] | One-to-four Family Residential Non-owner Occupied Loans [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	9,000	$ 9,000
Real Estate Portfolio Segment [Member] | One-to-four Family Residential Non-owner Occupied Loans [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 0
Real Estate Portfolio Segment [Member] | Multi-family (Five Or More) Residential Loans [Member]
Troubled debt restructuring, number of contracts	0	0
Troubled debt restructuring, recorded investment	$ 0	$ 0
Troubled debt restructuring, related allowance	0	0
Real Estate Portfolio Segment [Member] | Multi-family (Five Or More) Residential Loans [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	0	0
Real Estate Portfolio Segment [Member] | Multi-family (Five Or More) Residential Loans [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 0	$ 0
Real Estate Portfolio Segment [Member] | Commercial Real Estate Loans [Member]
Troubled debt restructuring, number of contracts	1	1
Troubled debt restructuring, recorded investment	$ 131,000	$ 131,000
Troubled debt restructuring, related allowance	0	0
Real Estate Portfolio Segment [Member] | Commercial Real Estate Loans [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	0
Real Estate Portfolio Segment [Member] | Commercial Real Estate Loans [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 131,000	$ 131,000
Real Estate Portfolio Segment [Member] | Construction Loans [Member]
Troubled debt restructuring, number of contracts	0	0
Troubled debt restructuring, recorded investment	$ 0	$ 0
Troubled debt restructuring, related allowance	0	0
Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	0	0
Real Estate Portfolio Segment [Member] | Construction Loans [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 0	$ 0
Real Estate Portfolio Segment [Member] | Home Equity Loan [Member]
Troubled debt restructuring, number of contracts	0	0
Troubled debt restructuring, recorded investment	$ 0	$ 0
Troubled debt restructuring, related allowance	0	0
Real Estate Portfolio Segment [Member] | Home Equity Loan [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	0	0
Real Estate Portfolio Segment [Member] | Home Equity Loan [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 0	$ 0
Commercial Portfolio Segment [Member]
Troubled debt restructuring, number of contracts	0	0
Troubled debt restructuring, recorded investment	$ 0	$ 0
Troubled debt restructuring, related allowance	0	0
Commercial Portfolio Segment [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	0	0
Commercial Portfolio Segment [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 0	$ 0
Consumer Portfolio Segment [Member]
Troubled debt restructuring, number of contracts	0	0
Troubled debt restructuring, recorded investment	$ 0	$ 0
Troubled debt restructuring, related allowance	0	0
Consumer Portfolio Segment [Member] | Nonaccruing Instrument [Member]
Troubled debt restructuring, recorded investment	0	0
Consumer Portfolio Segment [Member] | Accruing Instrument [Member]
Troubled debt restructuring, recorded investment	$ 0	$ 0