Credit Risk Ratings by Loan Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	$ 808,754	$ 651,642
1-4 Family
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	388,012	325,040
Multifamily
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	188,550	158,200
Nonresidential
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	151,193	121,500
Construction and Land
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	67,240	30,340
Business
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	12,873	15,719
Consumer
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	886	843
Pass
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	780,438	629,868
Pass | 1-4 Family
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	370,629	313,345
Pass | Multifamily
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	188,030	158,200
Pass | Nonresidential
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	148,253	117,467
Pass | Construction and Land
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	59,914	24,316
Pass | Business
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	12,726	15,697
Pass | Consumer
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	886	843
Special Mention
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	5,317	2,549
Special Mention | 1-4 Family
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	4,667	2,549
Special Mention | Construction and Land
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	650
Substandard
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	22,999	19,225
Substandard | 1-4 Family
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	12,716	9,146
Substandard | Multifamily
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	520
Substandard | Nonresidential
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	2,940	4,033
Substandard | Construction and Land
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	6,676	6,024
Substandard | Business
Financing Receivable Recorded Investment [Line Items]
Loans before net deferred loan origination cost and allowance for losses on loan	$ 147	$ 22