Loans Receivable and Related Allowance for Loan Losses - Aggregate Pass rating (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Classes of loan portfolio summarized within internal risk rating system
Loans	$ 749,147	$ 717,847
Pass
Classes of loan portfolio summarized within internal risk rating system
Loans	741,922	711,707
Special Mention
Classes of loan portfolio summarized within internal risk rating system
Loans	2,249	3,424
Substandard
Classes of loan portfolio summarized within internal risk rating system
Loans	4,976	2,716
Real Estate Loans | One-to-four-family Residential and Construction
Classes of loan portfolio summarized within internal risk rating system
Loans	212,447	234,421
Real Estate Loans | One-to-four-family Residential and Construction | Pass
Classes of loan portfolio summarized within internal risk rating system
Loans	210,367	232,354
Real Estate Loans | One-to-four-family Residential and Construction | Substandard
Classes of loan portfolio summarized within internal risk rating system
Loans	2,080	2,067
Real Estate Loans | Commercial Real Estate and Construction
Classes of loan portfolio summarized within internal risk rating system
Loans	343,485	323,843
Real Estate Loans | Commercial Real Estate and Construction | Pass
Classes of loan portfolio summarized within internal risk rating system
Loans	339,743	320,988
Real Estate Loans | Commercial Real Estate and Construction | Special Mention
Classes of loan portfolio summarized within internal risk rating system
Loans	1,141	2,544
Real Estate Loans | Commercial Real Estate and Construction | Substandard
Classes of loan portfolio summarized within internal risk rating system
Loans	2,601	311
Real Estate Loans | Home Equity Loans and Lines of Credit
Classes of loan portfolio summarized within internal risk rating system
Loans	103,699	111,499
Real Estate Loans | Home Equity Loans and Lines of Credit | Pass
Classes of loan portfolio summarized within internal risk rating system
Loans	103,421	111,165
Real Estate Loans | Home Equity Loans and Lines of Credit | Special Mention
Classes of loan portfolio summarized within internal risk rating system
Loans	59	62
Real Estate Loans | Home Equity Loans and Lines of Credit | Substandard
Classes of loan portfolio summarized within internal risk rating system
Loans	219	272
Commercial Business
Classes of loan portfolio summarized within internal risk rating system
Loans	88,975	47,514
Commercial Business | Pass
Classes of loan portfolio summarized within internal risk rating system
Loans	87,852	46,636
Commercial Business | Special Mention
Classes of loan portfolio summarized within internal risk rating system
Loans	1,049	818
Commercial Business | Substandard
Classes of loan portfolio summarized within internal risk rating system
Loans	74	60
Other Loans
Classes of loan portfolio summarized within internal risk rating system
Loans	541	570
Other Loans | Pass
Classes of loan portfolio summarized within internal risk rating system
Loans	539	564
Other Loans | Substandard
Classes of loan portfolio summarized within internal risk rating system
Loans	$ 2	$ 6