Loans Receivable, Part IV (Details) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Loans and Leases Receivable [Abstract]
At December 31, 2016	$ 1,433,803,000		$ 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	$ 212,000		224,000
Total Impaired, with no Reserve, Recorded Investment	8,325,000		9,833,000
Total Impaired, Recorded Investment	8,537,000		10,057,000
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	212,000		633,000
Total Impaired with no Reserve, Unpaid Principal Balance	10,159,000		11,680,000
Total Impaired, Unpaid Principal Balance, Total	10,371,000		12,313,000
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	27,000		39,000
Total Impaired with no Reserve, Reserve	0		0
Impaired Loans, Reserve	27,000		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	1,834,000		1,847,000
Total Impaired, Cumulative Charge-offs	1,834,000		2,256,000
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	215,000	$ 799,000
Total Impaired with no Reserve, Average Recorded Investment	8,436,000	8,099,000
Total Impaired, Average Recorded Investment, Total	8,651,000	8,898,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	8,000	32,000
Total Impaired with no Reserve, Interest Paid YTD	233,000	266,000
Total Impaired, Interest Paid YTD	241,000	298,000
Charge-offs recorded to reduce the unpaid principal balance	1,800,000
Total impaired loans including troubled debt restructurings	3,886,000		4,018,000
Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	9,457,000		11,013,000
Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	18,655,000		8,237,000
Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	1,405,691,000		1,368,781,000
Residential Real Estate [Member] | One-to-Four Family [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	467,346,000		480,280,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	212,000		217,000
Total Impaired, with no Reserve, Recorded Investment	7,266,000		8,508,000
Total Impaired, Recorded Investment	7,478,000		8,725,000
Impaired Loans Receivable, Unpaid Principal Balance [Abstract]
Total Impaired with Reserve, Unpaid Principal Balance	212,000		217,000
Total Impaired with no Reserve, Unpaid Principal Balance	8,283,000		9,531,000
Total Impaired, Unpaid Principal Balance, Total	8,495,000		9,748,000
Impaired Loans Receivable, Reserve [Abstract]
Total Impaired with Reserve, Reserve	27,000		32,000
Total Impaired with no Reserve, Reserve	0		0
Impaired Loans, Reserve	27,000		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	1,017,000		1,023,000
Total Impaired, Cumulative Charge-offs	1,017,000		1,023,000
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	215,000	353,000
Total Impaired with no Reserve, Average Recorded Investment	7,361,000	6,727,000
Total Impaired, Average Recorded Investment, Total	7,576,000	7,080,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	8,000	11,000
Total Impaired with no Reserve, Interest Paid YTD	189,000	213,000
Total Impaired, Interest Paid YTD	197,000	224,000
Total impaired loans including troubled debt restructurings	3,328,000		3,425,000
Residential Real Estate [Member] | One-to-Four Family [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	7,478,000		8,725,000
Residential Real Estate [Member] | One-to-Four Family [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	8,685,000		5,975,000
Residential Real Estate [Member] | One-to-Four Family [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	451,183,000		465,580,000
Residential Real Estate [Member] | Multi Family [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	598,924,000		584,859,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0		0
Total Impaired, with no Reserve, Recorded Investment	639,000		667,000
Total Impaired, Recorded Investment	639,000		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	1,456,000		1,491,000
Total Impaired, Unpaid Principal Balance, Total	1,456,000		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	817,000		824,000
Total Impaired, Cumulative Charge-offs	817,000		824,000
Impaired Loans Receivable, Average Recorded Investment [Abstract]
Total Impaired with Reserve, Average Recorded Investment	0	348,000
Total Impaired with no Reserve, Average Recorded Investment	650,000	935,000
Total Impaired, Average Recorded Investment, Total	650,000	1,283,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	16,000
Total Impaired with no Reserve, Interest Paid YTD	34,000	41,000
Total Impaired, Interest Paid YTD	34,000	57,000
Total impaired loans including troubled debt restructurings	282,000		308,000
Residential Real Estate [Member] | Multi Family [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	639,000		668,000
Residential Real Estate [Member] | Multi Family [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	0		0
Residential Real Estate [Member] | Multi Family [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	598,285,000		584,191,000
Residential Real Estate [Member] | Home Equity [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	16,409,000		18,071,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0		0
Total Impaired, with no Reserve, Recorded Investment	77,000		84,000
Total Impaired, Recorded Investment	77,000		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	77,000		84,000
Total Impaired, Unpaid Principal Balance, Total	77,000		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	85,000
Total Impaired with no Reserve, Average Recorded Investment	79,000	46,000
Total Impaired, Average Recorded Investment, Total	79,000	131,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	5,000
Total Impaired with no Reserve, Interest Paid YTD	2,000	2,000
Total Impaired, Interest Paid YTD	2,000	7,000
Residential Real Estate [Member] | Home Equity [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	265,000		285,000
Residential Real Estate [Member] | Home Equity [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	6,000		3,000
Residential Real Estate [Member] | Home Equity [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	16,138,000		17,783,000
Construction and Land [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	48,850,000		37,033,000
Impaired Loans Receivable, Recorded Investment [Abstract]
Total Impaired, with Reserve, Recorded Investment	0		0
Total Impaired, with no Reserve, Recorded Investment	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
Construction and Land [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	0		0
Construction and Land [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	3,494,000		0
Construction and Land [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	45,356,000		37,033,000
Commercial Real Estate [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	244,775,000		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	343,000		574,000
Total Impaired, Recorded Investment	343,000		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	343,000		574,000
Total Impaired, Unpaid Principal Balance, Total	343,000		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	13,000
Total Impaired with no Reserve, Average Recorded Investment	346,000	380,000
Total Impaired, Average Recorded Investment, Total	346,000	393,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	8,000	9,000
Total Impaired, Interest Paid YTD	8,000	9,000
Total impaired loans including troubled debt restructurings	276,000		285,000
Commercial Real Estate [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	343,000		581,000
Commercial Real Estate [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	5,090,000		1,412,000
Commercial Real Estate [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	239,342,000		234,710,000
Consumer [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	860,000		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, 2016	0		0
Consumer [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	0		0
Consumer [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	860,000		832,000
Commercial Loans [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	56,639,000		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	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	11,000
Total Impaired, Average Recorded Investment, Total	0	11,000
Impaired Loans Receivable, Interest Paid YTD [Abstract]
Total Impaired with Reserve, Interest Paid YTD	0	0
Total Impaired with no Reserve, Interest Paid YTD	0	1,000
Total Impaired, Interest Paid YTD	0	$ 1,000
Commercial Loans [Member] | Substandard [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	732,000		754,000
Commercial Loans [Member] | Watch [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	1,380,000		847,000
Commercial Loans [Member] | Pass [Member]
Loans and Leases Receivable [Abstract]
At December 31, 2016	$ 54,527,000		$ 28,652,000