Loans Receivable Held for Investment - Allowance for Loan Losses and Recorded Investment in Loans by Type of Loans and Based on Impairment Method (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Ending allowance balance attributable to loans:
Individually evaluated for impairment	$ 530	$ 585
Collectively evaluated for impairment	3,653	3,484
Total ending allowance balance	4,183	4,069	$ 4,392	$ 4,603
Loans:
Loans individually evaluated for impairment	8,890	9,305
Loans collectively evaluated for impairment	341,511	329,615
Gross loans receivable after deferred loan costs and premiums	350,401	338,920
Single family
Ending allowance balance attributable to loans:
Individually evaluated for impairment	84	100
Collectively evaluated for impairment	504	494
Total ending allowance balance	588	594	330	367
Loans:
Loans individually evaluated for impairment	622	627
Loans collectively evaluated for impairment	108,248	110,897
Gross loans receivable after deferred loan costs and premiums	108,870	111,524
Multi-family
Ending allowance balance attributable to loans:
Individually evaluated for impairment	1	1
Collectively evaluated for impairment	2,507	2,299
Total ending allowance balance	2,508	2,300	2,711	2,659
Loans:
Loans individually evaluated for impairment	331	333
Loans collectively evaluated for impairment	204,162	188,585
Gross loans receivable after deferred loan costs and premiums	204,493	188,918
Commercial real estate
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	65	71
Total ending allowance balance	65	71	75	215
Loans:
Loans collectively evaluated for impairment	5,826	6,096
Gross loans receivable after deferred loan costs and premiums	5,826	6,096
Church
Ending allowance balance attributable to loans:
Individually evaluated for impairment	440	479
Collectively evaluated for impairment	565	602
Total ending allowance balance	1,005	1,081	1,250	1,337
Loans:
Loans individually evaluated for impairment	7,873	8,280
Loans collectively evaluated for impairment	22,048	22,232
Gross loans receivable after deferred loan costs and premiums	29,921	30,512
Construction
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	11	17
Total ending allowance balance	11	17	9	8
Loans:
Loans collectively evaluated for impairment	1,092	1,671
Gross loans receivable after deferred loan costs and premiums	1,092	1,671
Commercial - other
Ending allowance balance attributable to loans:
Individually evaluated for impairment	5	5
Collectively evaluated for impairment	1	1
Total ending allowance balance	6	6	16	$ 17
Loans:
Loans individually evaluated for impairment	64	65
Loans collectively evaluated for impairment	131	127
Gross loans receivable after deferred loan costs and premiums	195	192
Consumer
Ending allowance balance attributable to loans:
Total ending allowance balance			$ 1
Loans:
Loans collectively evaluated for impairment	4	7
Gross loans receivable after deferred loan costs and premiums	$ 4	$ 7