Loans Receivable, Part IV (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable [Abstract]
At December 31, 2020	$ 1,375,137,000	$ 1,388,031,000
Loans requiring an officers' loans committee review and approval, minimum	500,000
Minimum amount of potential loan exposure to be reviewed by credit management personnel	$ 1,000,000.0
Maximum period of time loan is reviewed if renewed	1 year
Period of time sales of real estate owned fair value is based	2 years
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	$ 208,000	224,000
Total Impaired, with no Reserve, Recorded Investment	16,389,000	9,833,000
Total Impaired, Recorded Investment	16,597,000	10,057,000
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	208,000	633,000
Total Impaired with no Reserve, Unpaid Principal Balance	17,255,000	11,680,000
Total Impaired, Unpaid Principal Balance, Total	17,463,000	12,313,000
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	23,000	39,000
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	23,000	39,000
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	409,000
Total Impaired with no Reserve, Cumulative Charge-offs	866,000	1,847,000
Total Impaired, Cumulative Charge-offs	866,000	2,256,000
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	213,000	231,000
Total Impaired with no Reserve, Average Recorded Investment	16,633,000	10,170,000
Total Impaired, Average Recorded Investment, Total	16,846,000	10,401,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	15,000	15,000
Total Impaired with no Reserve, Interest Paid YTD	706,000	616,000
Total Impaired, Interest Paid YTD	721,000	631,000
Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	15,172,000	11,013,000
Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	23,054,000	8,237,000
Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	1,336,911,000	1,368,781,000
Residential Real Estate [Member] | One-to-Four Family [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	426,792,000	480,280,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	208,000	217,000
Total Impaired, with no Reserve, Recorded Investment	7,597,000	8,508,000
Total Impaired, Recorded Investment	7,805,000	8,725,000
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	208,000	217,000
Total Impaired with no Reserve, Unpaid Principal Balance	8,444,000	9,531,000
Total Impaired, Unpaid Principal Balance, Total	8,652,000	9,748,000
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	23,000	32,000
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	23,000	32,000
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	0
Total Impaired with no Reserve, Cumulative Charge-offs	847,000	1,023,000
Total Impaired, Cumulative Charge-offs	847,000	1,023,000
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	213,000	221,000
Total Impaired with no Reserve, Average Recorded Investment	7,770,000	8,730,000
Total Impaired, Average Recorded Investment, Total	7,983,000	8,951,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	15,000	15,000
Total Impaired with no Reserve, Interest Paid YTD	349,000	508,000
Total Impaired, Interest Paid YTD	364,000	523,000
Residential Real Estate [Member] | One-to-Four Family [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	7,804,000	8,725,000
Residential Real Estate [Member] | One-to-Four Family [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	7,667,000	5,975,000
Residential Real Estate [Member] | One-to-Four Family [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	411,321,000	465,580,000
Residential Real Estate [Member] | Multi Family [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	571,948,000	584,859,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0	0
Total Impaired, with no Reserve, Recorded Investment	341,000	667,000
Total Impaired, Recorded Investment	341,000	667,000
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	0	0
Total Impaired with no Reserve, Unpaid Principal Balance	352,000	1,491,000
Total Impaired, Unpaid Principal Balance, Total	352,000	1,491,000
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	0	0
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	0	0
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	0
Total Impaired with no Reserve, Cumulative Charge-offs	11,000	824,000
Total Impaired, Cumulative Charge-offs	11,000	824,000
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	0	0
Total Impaired with no Reserve, Average Recorded Investment	353,000	705,000
Total Impaired, Average Recorded Investment, Total	353,000	705,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	17,000	78,000
Total Impaired, Interest Paid YTD	17,000	78,000
Residential Real Estate [Member] | Multi Family [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	341,000	668,000
Residential Real Estate [Member] | Multi Family [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	275,000	0
Residential Real Estate [Member] | Multi Family [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	571,332,000	584,191,000
Residential Real Estate [Member] | Home Equity [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	14,820,000	18,071,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0	0
Total Impaired, with no Reserve, Recorded Investment	63,000	84,000
Total Impaired, Recorded Investment	63,000	84,000
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	0	0
Total Impaired with no Reserve, Unpaid Principal Balance	63,000	84,000
Total Impaired, Unpaid Principal Balance, Total	63,000	84,000
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	0	0
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	0	0
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	0
Total Impaired with no Reserve, Cumulative Charge-offs	0	0
Total Impaired, Cumulative Charge-offs	0	0
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	0	0
Total Impaired with no Reserve, Average Recorded Investment	67,000	88,000
Total Impaired, Average Recorded Investment, Total	67,000	88,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	4,000	7,000
Total Impaired, Interest Paid YTD	4,000	7,000
Residential Real Estate [Member] | Home Equity [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	248,000	285,000
Residential Real Estate [Member] | Home Equity [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	15,000	3,000
Residential Real Estate [Member] | Home Equity [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	14,557,000	17,783,000
Construction and Land [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	77,080,000	37,033,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0	0
Total Impaired, with no Reserve, Recorded Investment	43,000	0
Total Impaired, Recorded Investment	43,000	0
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	0	0
Total Impaired with no Reserve, Unpaid Principal Balance	51,000	0
Total Impaired, Unpaid Principal Balance, Total	51,000	0
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	0	0
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	0	0
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	0
Total Impaired with no Reserve, Cumulative Charge-offs	8,000	0
Total Impaired, Cumulative Charge-offs	8,000	0
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	0	0
Total Impaired with no Reserve, Average Recorded Investment	51,000	0
Total Impaired, Average Recorded Investment, Total	51,000	0
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	1,000	0
Total Impaired, Interest Paid YTD	1,000	0
Construction and Land [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	43,000	0
Construction and Land [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	4,282,000	0
Construction and Land [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	72,755,000	37,033,000
Commercial Real Estate [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	238,375,000	236,703,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0	7,000
Total Impaired, with no Reserve, Recorded Investment	7,248,000	574,000
Total Impaired, Recorded Investment	7,248,000	581,000
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	0	416,000
Total Impaired with no Reserve, Unpaid Principal Balance	7,248,000	574,000
Total Impaired, Unpaid Principal Balance, Total	7,248,000	990,000
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	0	7,000
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	0	7,000
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	409,000
Total Impaired with no Reserve, Cumulative Charge-offs	0	0
Total Impaired, Cumulative Charge-offs	0	409,000
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	0	10,000
Total Impaired with no Reserve, Average Recorded Investment	7,295,000	647,000
Total Impaired, Average Recorded Investment, Total	7,295,000	657,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	333,000	23,000
Total Impaired, Interest Paid YTD	333,000	23,000
Commercial Real Estate [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	6,026,000	581,000
Commercial Real Estate [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	6,714,000	1,412,000
Commercial Real Estate [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	225,635,000	234,710,000
Consumer [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	736,000	832,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0	0
Total Impaired, with no Reserve, Recorded Investment	0	0
Total Impaired, Recorded Investment	0	0
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	0	0
Total Impaired with no Reserve, Unpaid Principal Balance	0	0
Total Impaired, Unpaid Principal Balance, Total	0	0
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	0	0
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	0	0
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	0
Total Impaired with no Reserve, Cumulative Charge-offs	0	0
Total Impaired, Cumulative Charge-offs	0	0
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	0	0
Total Impaired with no Reserve, Average Recorded Investment	0	0
Total Impaired, Average Recorded Investment, Total	0	0
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	0	0
Total Impaired, Interest Paid YTD	0	0
Consumer [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	0	0
Consumer [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	0	0
Consumer [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	736,000	832,000
Commercial [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	45,386,000	30,253,000
Minimum amount of potential loan exposure to be reviewed by credit management personnel	200,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0	0
Total Impaired, with no Reserve, Recorded Investment	1,097,000	0
Total Impaired, Recorded Investment	1,097,000	0
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	0	0
Total Impaired with no Reserve, Unpaid Principal Balance	1,097,000	0
Total Impaired, Unpaid Principal Balance, Total	1,097,000	0
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	0	0
Total Impaired with no Reserve, Reserve	0	0
Impaired Loans, Reserve	0	0
Impaired Loans Receivable, Cumulative Charge-Offs [Abstract]
Total Impaired with Reserve, Cumulative Charge-offs	0	0
Total Impaired with no Reserve, Cumulative Charge-offs	0	0
Total Impaired, Cumulative Charge-offs	0	0
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	0	0
Total Impaired with no Reserve, Average Recorded Investment	1,097,000	0
Total Impaired, Average Recorded Investment, Total	1,097,000	0
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	2,000	0
Total Impaired, Interest Paid YTD	2,000	0
Commercial [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	710,000	754,000
Commercial [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	4,101,000	847,000
Commercial [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2020	$ 40,575,000	$ 28,652,000