Loans and Allowance for Loan Losses - Risk category of our loan portfolio (Details) $ in Thousands	Sep. 30, 2020 USD ($)
2020	$ 591,683
2019	913,660
2018	972,833
2017	736,161
2016	651,192
Prior	1,841,327
Revolving Loans Amortized Cost Basis	212,208
Lines of credit converted to term loans	22,334
One-To-Four Family - Residential Portfolio Segment [Member]
2020	23,224
2019	25,030
2018	27,827
2017	15,548
2016	12,191
Prior	66,650
Revolving Loans Amortized Cost Basis	7,977
Lines of credit converted to term loans	22,334
One-To-Four Family - Residential Portfolio Segment [Member] \| Pass [Member]
2020	22,735
2019	25,030
2018	27,827
2017	15,548
2016	11,231
Prior	59,657
Revolving Loans Amortized Cost Basis	7,678
Lines of credit converted to term loans	18,095
One-To-Four Family - Residential Portfolio Segment [Member] \| Watch [Member]
2020	489
Prior	2,936
Revolving Loans Amortized Cost Basis	299
Lines of credit converted to term loans	2,011
One-To-Four Family - Residential Portfolio Segment [Member] \| Special Mention [Member]
Prior	667
Lines of credit converted to term loans	492
One-To-Four Family - Residential Portfolio Segment [Member] \| Substandard [Member]
2016	960
Prior	3,390
Lines of credit converted to term loans	1,736
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member]
2020	27,156
2019	68,993
2018	76,916
2017	61,936
2016	54,490
Prior	300,107
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Pass [Member]
2020	27,156
2019	66,500
2018	74,828
2017	59,923
2016	53,344
Prior	288,858
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Watch [Member]
2019	1,873
2018	903
2017	2,013
2016	1,146
Prior	8,556
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Special Mention [Member]
2018	379
Prior	1,179
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Substandard [Member]
2019	620
2018	806
Prior	1,514
Commercial Real Estate Portfolio Segment [Member]
2020	118,019
2019	260,101
2018	281,920
2017	194,667
2016	241,756
Prior	542,954
Commercial Real Estate Portfolio Segment [Member] \| Pass [Member]
2020	118,019
2019	248,812
2018	281,920
2017	189,592
2016	213,553
Prior	482,495
Commercial Real Estate Portfolio Segment [Member] \| Watch [Member]
2019	8,606
2017	4,883
2016	28,203
Prior	58,587
Commercial Real Estate Portfolio Segment [Member] \| Special Mention [Member]
2019	981
2017	192
Prior	861
Commercial Real Estate Portfolio Segment [Member] \| Substandard [Member]
2019	1,702
Prior	1,011
Construction Portfolio Segment [Member]
2020	10,058
2019	15,637
2018	37,711
Construction Portfolio Segment [Member] \| Pass [Member]
2020	10,058
2019	14,751
2018	31,402
Construction Portfolio Segment [Member] \| Watch [Member]
2019	886
2018	5,631
Construction Portfolio Segment [Member] \| Special Mention [Member]
2018	678
Multi-family Residential Portfolio Segment [Member]
2020	174,397
2019	311,135
2018	366,297
2017	358,743
2016	272,871
Prior	771,711
Revolving Loans Amortized Cost Basis	4,298
Multi-family Residential Portfolio Segment [Member] \| Pass [Member]
2020	174,397
2019	309,564
2018	364,298
2017	356,206
2016	269,388
Prior	749,946
Revolving Loans Amortized Cost Basis	3,433
Multi-family Residential Portfolio Segment [Member] \| Watch [Member]
2019	1,571
2017	2,537
2016	2,784
Prior	19,504
Revolving Loans Amortized Cost Basis	865
Multi-family Residential Portfolio Segment [Member] \| Special Mention [Member]
2016	699
Prior	776
Multi-family Residential Portfolio Segment [Member] \| Substandard [Member]
2018	1,999
Prior	1,485
Commercial Business Secured By Portfolio Segment [member]
2020	68,713
2019	91,282
2018	63,784
2017	23,371
2016	47,335
Prior	86,115
Commercial Business Secured By Portfolio Segment [member] \| Pass [Member]
2020	68,713
2019	91,282
2018	56,704
2017	22,051
2016	47,335
Prior	82,368
Commercial Business Secured By Portfolio Segment [member] \| Watch [Member]
2018	7,080
2017	1,320
Prior	416
Commercial Business Secured By Portfolio Segment [member] \| Substandard [Member]
Prior	3,331
Commercial Business Portfolio Segment [Member]
2020	59,995
2019	140,415
2018	114,788
2017	77,427
2016	19,991
Prior	69,661
Revolving Loans Amortized Cost Basis	199,834
Commercial Business Portfolio Segment [Member] \| Pass [Member]
2020	59,956
2019	137,475
2018	108,265
2017	64,737
2016	17,573
Prior	67,940
Revolving Loans Amortized Cost Basis	186,882
Commercial Business Portfolio Segment [Member] \| Watch [Member]
2019	2,889
2018	4,112
2017	7,880
Prior	10
Revolving Loans Amortized Cost Basis	10,935
Commercial Business Portfolio Segment [Member] \| Special Mention [Member]
2019	51
2018	2,411
2016	2,418
Revolving Loans Amortized Cost Basis, Net	(26)
Commercial Business Portfolio Segment [Member] \| Substandard [Member]
2020	39
2017	4,810
Prior	1,711
Revolving Loans Amortized Cost Basis	171
Commercial Business Portfolio Segment [Member] \| Doubtful [Member]
Revolving Loans Amortized Cost Basis	1,872
Small Business Administration Portfolio Segment [Member]
2020	110,121
2019	1,067
2018	3,590
2017	4,469
2016	2,558
Prior	1,675
Small Business Administration Portfolio Segment [Member] \| Pass [Member]
2020	110,121
2019	1,067
2018	3,590
2017	1,043
2016	2,551
Prior	1,625
Small Business Administration Portfolio Segment [Member] \| Watch [Member]
2017	2,257
Small Business Administration Portfolio Segment [Member] \| Special Mention [Member]
Prior	50
Small Business Administration Portfolio Segment [Member] \| Substandard [Member]
2017	1,169
2016	7
Taxi Medallion Portfolio Segment [Member]
Prior	2,318
Taxi Medallion Portfolio Segment [Member] \| Substandard [Member]
Prior	2,318
Other Portfolio Segment [Member]
Prior	136
Revolving Loans Amortized Cost Basis	99
Other Portfolio Segment [Member] \| Pass [Member]
Prior	136
Revolving Loans Amortized Cost Basis	$ 99

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