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Loans Receivable - Loans Individually Evaluated for Impairment (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2019 | Dec. 31, 2018 | Jun. 30, 2019 | Sep. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | $ 1,220,609,000 | $ 1,220,609,000 | $ 1,331,194,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Loan Balance |  |  | 3,491,000 |  |  |  |
Recorded Investment |  |  | 2,854,000 |  |  |  |
Partial Charge-off |  |  | 618,000 |  |  |  |
Average Investment in Impaired Loans |  |  | 4,164,000 |  |  |  |
Interest Income Recognized |  |  | 80,000 |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 27,000 |  |  |  |
Impaired Loan, Total | 3,857,000 | 3,857,000 | 3,847,000 |  |  |  |
Recorded Investment, Total | 3,328,000 | 3,328,000 | 3,124,000 |  |  |  |
Partial Charge-offs, Total | 542,000 | 542,000 | 711,000 |  |  |  |
Average Investment in Impaired Loans, Total | 4,494,000 | 3,668,000 | 4,185,000 |  |  |  |
Interest Income Recognized, Total | 21,000 | 70,000 | 80,000 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 7,603,000 | 7,603,000 | 8,443,000 |  |  |  |
Net deferred loan origination costs | 942,000 | 942,000 | 1,069,000 |  |  |  |
Loans and Leases Receivable, Allowance | 7,603,000 | 7,603,000 | 8,470,000 | $ 7,824,000 | $ 8,103,000 | $ 8,179,000 | $ 8,366,000
Financing Receivable, Individually Evaluated for Impairment | 3,328,000 | 3,328,000 | 3,141,000 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 1,217,281,000 | 1,217,281,000 | 1,328,053,000 |  |  |  |
Loans, net | 1,213,948,000 | 1,213,948,000 | 1,323,793,000 |  |  |  |
One-to-four family residential real estate loans [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 60,757,000 | 60,757,000 | 70,371,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Loan Balance | 2,812,000 | 2,812,000 | 2,751,000 |  |  |  |
Recorded Investment | 2,280,000 | 2,280,000 | 2,155,000 |  |  |  |
Partial Charge-off | 542,000 | 542,000 | 575,000 |  |  |  |
Average Investment in Impaired Loans | 2,253,000 | 2,245,000 | 3,274,000 |  |  |  |
Interest Income Recognized | 12,000 | 40,000 | 41,000 |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 0 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 580,000 | 580,000 | 699,000 |  |  |  |
Loans and Leases Receivable, Allowance | 580,000 | 580,000 | 699,000 |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 2,416,000 | 2,416,000 | 2,218,000 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 58,341,000 | 58,341,000 | 68,153,000 |  |  |  |
One-to-four family residential real estate loans - non-owner occupied loans [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 11,432,000 | 11,432,000 | 13,202,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Loan Balance | 136,000 | 136,000 | 86,000 |  |  |  |
Recorded Investment | 136,000 | 136,000 | 46,000 |  |  |  |
Partial Charge-off | 0 | 0 | 43,000 |  |  |  |
Average Investment in Impaired Loans | 161,000 | 102,000 | 95,000 |  |  |  |
Interest Income Recognized | 0 | 1,000 | 0 |  |  |  |
Multi-family mortgage loans [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 577,656,000 | 577,656,000 | 619,870,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Loan Balance | 629,000 | 629,000 | 654,000 |  |  |  |
Recorded Investment | 630,000 | 630,000 | 653,000 |  |  |  |
Partial Charge-off | 0 | 0 | 0 |  |  |  |
Average Investment in Impaired Loans | 633,000 | 642,000 | 795,000 |  |  |  |
Interest Income Recognized | 9,000 | 28,000 | 39,000 |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 0 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 3,728,000 | 3,728,000 | 3,991,000 |  |  |  |
Loans and Leases Receivable, Allowance | 3,728,000 | 3,728,000 | 3,991,000 |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 630,000 | 630,000 | 653,000 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 577,026,000 | 577,026,000 | 619,217,000 |  |  |  |
Multi Family Mortgage Loans without wholesale [Member] [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 257,901,000 | 257,901,000 | 279,237,000 |  |  |  |
Wholesale commercial lending [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 319,755,000 | 319,755,000 | 340,633,000 |  |  |  |
Nonresidential real estate loans [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 140,410,000 | 140,410,000 | 152,442,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Loan Balance | 280,000 | 280,000 |  |  |  |  |
Recorded Investment | 282,000 | 282,000 |  |  |  |  |
Partial Charge-off | 0 | 0 |  |  |  |  |
Average Investment in Impaired Loans | 1,447,000 | 679,000 |  |  |  |  |
Interest Income Recognized | 0 | 1,000 |  |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 27,000 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 1,217,000 | 1,217,000 | 1,449,000 |  |  |  |
Loans and Leases Receivable, Allowance | 1,217,000 | 1,217,000 | 1,476,000 |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 282,000 | 282,000 | 270,000 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 140,128,000 | 140,128,000 | 152,172,000 |  |  |  |
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance |  |  | 356,000 |  |  |  |
Impaired Financing Receivable, with Related Allowance, Recorded Investment |  |  | 270,000 |  |  |  |
Impaired Financing Receivable, with Related Allowance, Partial Charge-offs |  |  | 93,000 |  |  |  |
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment |  |  | 21,000 |  |  |  |
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method |  |  | 0 |  |  |  |
Land loans [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 88,000 | 88,000 | 172,000 |  |  |  |
Commercial loans - Secured [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 28,094,000 | 28,094,000 | 39,574,000 |  |  |  |
Commercial loans - other [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 142,751,000 | 142,751,000 | 133,185,000 |  |  |  |
Consumer loans [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 2,052,000 | 2,052,000 | 1,539,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 0 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 36,000 | 36,000 | 28,000 |  |  |  |
Loans and Leases Receivable, Allowance | 36,000 | 36,000 | 28,000 |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 0 | 0 | 0 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 2,052,000 | 2,052,000 | 1,539,000 |  |  |  |
Construction And Land Loans [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 88,000 | 88,000 | 172,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 0 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 2,000 | 2,000 | 4,000 |  |  |  |
Loans and Leases Receivable, Allowance | 2,000 | 2,000 | 4,000 |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 0 | 0 | 0 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 88,000 | 88,000 | 172,000 |  |  |  |
Commercial Loan [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 163,846,000 | 163,846,000 | 187,406,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 0 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 1,308,000 | 1,308,000 | 1,517,000 |  |  |  |
Loans and Leases Receivable, Allowance | 1,308,000 | 1,308,000 | 1,517,000 |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 0 | 0 | 0 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 163,846,000 | 163,846,000 | 187,406,000 |  |  |  |
Finance Leases Financing Receivable [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | 275,800,000 | 275,800,000 | 299,394,000 |  |  |  |
Loans individually evaluated for impairment by class loans |  |  |  |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 | 0 |  |  |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 732,000 | 732,000 | 755,000 |  |  |  |
Loans and Leases Receivable, Allowance | 732,000 | 732,000 | 755,000 |  |  |  |
Financing Receivable, Individually Evaluated for Impairment | 0 | 0 | 0 |  |  |  |
Financing Receivable, Collectively Evaluated for Impairment | 275,800,000 | 275,800,000 | 299,394,000 |  |  |  |
One to Four Family Residential Real Estate Loans-Owner occupied [Member] [Member] |  |  |  |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  |  |  |
Total loans | $ 49,325,000 | $ 49,325,000 | $ 57,169,000 |  |  |  |

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