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Loans Receivable - Loans Individually Evaluated for Impairment (Details) - USD ($) | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018 | Mar. 31, 2018 | Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | $ 1,313,767,000 | $ 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 | 27,000 |  |
Impaired Loan, Total | 4,337,000 | 3,847,000 |  |
Recorded Investment, Total | 3,580,000 | 3,124,000 |  |
Partial Charge-offs, Total | 738,000 | 711,000 |  |
Average Investment in Impaired Loans, Total | 3,074,000 | 4,185,000 |  |
Interest Income Recognized, Total | 30,000 | 80,000 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 8,354,000 | 8,443,000 |  |
Net deferred loan origination costs | 1,062,000 | 1,069,000 |  |
Loans and Leases Receivable, Allowance | 8,354,000 | 8,470,000 | $ 8,341,000 | $ 8,366,000
Financing Receivable, Individually Evaluated for Impairment | 3,607,000 | 3,141,000 |  |
Financing Receivable, Collectively Evaluated for Impairment | 1,310,160,000 | 1,328,053,000 |  |
Loans, net | 1,306,475,000 | 1,323,793,000 |  |
One-to-four family residential real estate loans [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 66,833,000 | 70,371,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Loan Balance | 2,896,000 | 2,751,000 |  |
Recorded Investment | 2,303,000 | 2,155,000 |  |
Partial Charge-off | 561,000 | 575,000 |  |
Average Investment in Impaired Loans | 2,230,000 | 3,274,000 |  |
Interest Income Recognized | 15,000 | 41,000 |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 649,000 | 699,000 |  |
Loans and Leases Receivable, Allowance | 649,000 | 699,000 |  |
Financing Receivable, Individually Evaluated for Impairment | 2,365,000 | 2,218,000 |  |
Financing Receivable, Collectively Evaluated for Impairment | 64,468,000 | 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 | 12,531,000 | 13,202,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Loan Balance | 86,000 | 86,000 |  |
Recorded Investment | 32,000 | 46,000 |  |
Partial Charge-off | 56,000 | 43,000 |  |
Average Investment in Impaired Loans | 43,000 | 95,000 |  |
Interest Income Recognized | 0 | 0 |  |
Multi-family mortgage loans [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 634,328,000 | 619,870,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Loan Balance | 645,000 | 654,000 |  |
Recorded Investment | 649,000 | 653,000 |  |
Partial Charge-off | 0 | 0 |  |
Average Investment in Impaired Loans | 651,000 | 795,000 |  |
Interest Income Recognized | 9,000 | 39,000 |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 4,079,000 | 3,991,000 |  |
Loans and Leases Receivable, Allowance | 4,079,000 | 3,991,000 |  |
Financing Receivable, Individually Evaluated for Impairment | 646,000 | 653,000 |  |
Financing Receivable, Collectively Evaluated for Impairment | 633,682,000 | 619,217,000 |  |
Multi Family Mortgage Loans without wholesale [Member] [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 274,582,000 | 279,237,000 |  |
Wholesale commercial lending [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 359,746,000 | 340,633,000 |  |
Nonresidential real estate loans [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 148,601,000 | 152,442,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Loan Balance | 356,000 |  |  |
Recorded Investment | 242,000 |  |  |
Partial Charge-off | 121,000 |  |  |
Average Investment in Impaired Loans | 61,000 |  |  |
Interest Income Recognized | 0 |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 27,000 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 1,487,000 | 1,449,000 |  |
Loans and Leases Receivable, Allowance | 1,487,000 | 1,476,000 |  |
Financing Receivable, Individually Evaluated for Impairment | 242,000 | 270,000 |  |
Financing Receivable, Collectively Evaluated for Impairment | 148,359,000 | 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 | 145,000 | 172,000 |  |
Commercial loans - Secured [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 37,639,000 | 39,574,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Loan Balance | 354,000 |  |  |
Recorded Investment | 354,000 |  |  |
Partial Charge-off | 0 |  |  |
Average Investment in Impaired Loans | 89,000 |  |  |
Interest Income Recognized | 6,000 |  |  |
Commercial loans - other [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 132,535,000 | 133,185,000 |  |
Consumer loans [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 1,846,000 | 1,539,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 24,000 | 28,000 |  |
Loans and Leases Receivable, Allowance | 24,000 | 28,000 |  |
Financing Receivable, Individually Evaluated for Impairment | 0 | 0 |  |
Financing Receivable, Collectively Evaluated for Impairment | 1,846,000 | 1,539,000 |  |
Construction And Land Loans [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 145,000 | 172,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 3,000 | 4,000 |  |
Loans and Leases Receivable, Allowance | 3,000 | 4,000 |  |
Financing Receivable, Individually Evaluated for Impairment | 0 | 0 |  |
Financing Receivable, Collectively Evaluated for Impairment | 145,000 | 172,000 |  |
Commercial Loan [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 172,264,000 | 187,406,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 1,422,000 | 1,517,000 |  |
Loans and Leases Receivable, Allowance | 1,422,000 | 1,517,000 |  |
Financing Receivable, Individually Evaluated for Impairment | 354,000 | 0 |  |
Financing Receivable, Collectively Evaluated for Impairment | 171,910,000 | 187,406,000 |  |
Finance Leases Financing Receivable [Member] |  |  |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |
Total loans | 289,750,000 | 299,394,000 |  |
Loans individually evaluated for impairment by class loans |  |  |  |
Allowance for loan losses (With an allowance recorded) | 0 | 0 |  |
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment | 690,000 | 755,000 |  |
Loans and Leases Receivable, Allowance | 690,000 | 755,000 |  |
Financing Receivable, Individually Evaluated for Impairment | 0 | 0 |  |
Financing Receivable, Collectively Evaluated for Impairment | 289,750,000 | 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 | $ 54,302,000 | $ 57,169,000 |  |

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