Loans and Allowance for Loan Losses - Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Recorded investment, with no related allowance recorded	$ 16,170	$ 18,869
Unpaid principal balance, with no related allowance recorded	22,718	28,156
Recorded investment, with an allowance recorded	3,414	6,650
Unpaid principal balance, with an allowance recorded	3,414	6,650
Related allowance	315	1,160
Loans designated as criticized or classified	38,046	53,030
Average Recorded Investment, With no related allowance recorded	18,374	36,121	$ 31,023
Interest Income Recognized, With no related allowance recorded	296	1,558	948
Average Recorded Investment, With an allowance recorded	4,075	4,525	17,507
Interest Income Recognized, With an allowance recorded	122	191	500
Mortgage Receivable [Member]
Related allowance	183	294
Loans designated as criticized or classified	12,238	15,922
Unpaid principal balance, total impaired loans	12,298	16,618
Average Recorded Investment, Total Impaired Loans	14,640	22,722	31,147
Interest Income Recognized, Total Impaired Loans	247	586	990
Non-Mortgage Loans [Member]
Related allowance	132	866
Loans designated as criticized or classified	7,346	9,597
Unpaid principal balance, total impaired loans	13,834	18,188
Average Recorded Investment, Total Impaired Loans	7,809	17,924	17,383
Interest Income Recognized, Total Impaired Loans	171	1,163	458
Multi-family Residential Portfolio Segment [Member]
Loans designated as criticized or classified	4,306	6,664
Multi-family Residential Portfolio Segment [Member] \| Mortgage Receivable [Member]
Recorded investment, with no related allowance recorded	2,919	3,225
Unpaid principal balance, with no related allowance recorded	2,919	3,568
Recorded investment, with an allowance recorded	1,250	1,275
Unpaid principal balance, with an allowance recorded	1,250	1,275
Related allowance	92	100
Average Recorded Investment, With no related allowance recorded	3,155	3,957	3,260
Interest Income Recognized, With no related allowance recorded	36	76	80
Average Recorded Investment, With an allowance recorded	1,263	1,741	2,348
Interest Income Recognized, With an allowance recorded	72	96	136
Commercial Real Estate Portfolio Segment [Member]
Loans designated as criticized or classified	5,892	4,432
Commercial Real Estate Portfolio Segment [Member] \| Mortgage Receivable [Member]
Recorded investment, with no related allowance recorded	367	1,435
Unpaid principal balance, with no related allowance recorded	367	1,435
Average Recorded Investment, With no related allowance recorded	1,081	4,334	6,187
Interest Income Recognized, With no related allowance recorded	15	176	300
Average Recorded Investment, With an allowance recorded	0	0	2,026
Interest Income Recognized, With an allowance recorded	0	0	95
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member]
Loans designated as criticized or classified	2,038	3,233
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Mortgage Receivable [Member]
Recorded investment, with no related allowance recorded	921	1,913
Unpaid principal balance, with no related allowance recorded	924	2,113
Recorded investment, with an allowance recorded	840	1,185
Unpaid principal balance, with an allowance recorded	840	1,185
Related allowance	45	143
Average Recorded Investment, With no related allowance recorded	1,719	3,298	5,104
Interest Income Recognized, With no related allowance recorded	67	125	168
Average Recorded Investment, With an allowance recorded	975	1,201	1,341
Interest Income Recognized, With an allowance recorded	34	54	65
One-To-Four Family - Residential Portfolio Segment [Member]
Loans designated as criticized or classified	6,882	7,222
One-To-Four Family - Residential Portfolio Segment [Member] \| Mortgage Receivable [Member]
Recorded investment, with no related allowance recorded	5,558	6,490
Unpaid principal balance, with no related allowance recorded	5,615	6,643
Recorded investment, with an allowance recorded	383	399
Unpaid principal balance, with an allowance recorded	383	399
Related allowance	46	51
Average Recorded Investment, With no related allowance recorded	5,866	7,603	9,865
Interest Income Recognized, With no related allowance recorded	7	33	108
Average Recorded Investment, With an allowance recorded	391	405	420
Interest Income Recognized, With an allowance recorded	16	16	16
Construction Portfolio Segment [Member]
Loans designated as criticized or classified		730
Construction Portfolio Segment [Member] \| Mortgage Receivable [Member]
Average Recorded Investment, With no related allowance recorded	190	183	596
Interest Income Recognized, With no related allowance recorded	0	10	22
Small Business Administration Portfolio Segment [Member]
Loans designated as criticized or classified	140	620
Small Business Administration Portfolio Segment [Member] \| Non-Mortgage Loans [Member]
Recorded investment, with no related allowance recorded	1,151	1,267
Unpaid principal balance, with no related allowance recorded	1,421	1,609
Average Recorded Investment, With no related allowance recorded	1,204	711	207
Interest Income Recognized, With no related allowance recorded	0	33	11
Taxi Medallion Portfolio Segment [Member]
Loans designated as criticized or classified	3,309	4,539
Taxi Medallion Portfolio Segment [Member] \| Non-Mortgage Loans [Member]
Recorded investment, with no related allowance recorded	3,309	4,539
Unpaid principal balance, with no related allowance recorded	9,527	12,788
Average Recorded Investment, With no related allowance recorded	3,761	5,865	4,537
Interest Income Recognized, With no related allowance recorded	171	313	161
Average Recorded Investment, With an allowance recorded	0	0	10,997
Interest Income Recognized, With an allowance recorded	0	0	166
Commercial Business and Other Portfolio Segment [Member]
Loans designated as criticized or classified	15,479	25,590
Commercial Business and Other Portfolio Segment [Member] \| Mortgage Receivable [Member]
Recorded investment, with an allowance recorded	941	3,791
Unpaid principal balance, with an allowance recorded	941	3,791
Related allowance	132	866
Commercial Business and Other Portfolio Segment [Member] \| Non-Mortgage Loans [Member]
Recorded investment, with no related allowance recorded	1,945	0
Unpaid principal balance, with no related allowance recorded	1,945	0
Average Recorded Investment, With no related allowance recorded	1,398	10,170	1,267
Interest Income Recognized, With no related allowance recorded	0	792	98
Average Recorded Investment, With an allowance recorded	1,446	1,178	375
Interest Income Recognized, With an allowance recorded	$ 0	$ 25	$ 22

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

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