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	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Ending allowance balance attributable to loans:
Individually evaluated for impairment	$ 501		$ 585
Collectively evaluated for impairment	3,682		3,484
Total ending allowance balance	4,183	$ 4,183	4,069	$ 4,246	$ 4,392	$ 4,603
Loans:
Loans individually evaluated for impairment	8,564		9,305
Loans collectively evaluated for impairment	360,427		329,615
Gross loans receivable after deferred loan costs and premiums	368,991		338,920
Single family
Ending allowance balance attributable to loans:
Individually evaluated for impairment	82		100
Collectively evaluated for impairment	435		494
Total ending allowance balance	517	588	594	320	330	367
Loans:
Loans individually evaluated for impairment	618		627
Loans collectively evaluated for impairment	99,399		110,897
Gross loans receivable after deferred loan costs and premiums	100,017		111,524
Multi-family
Ending allowance balance attributable to loans:
Individually evaluated for impairment			1
Collectively evaluated for impairment	2,656		2,299
Total ending allowance balance	2,656	2,508	2,300	2,719	2,711	2,659
Loans:
Loans individually evaluated for impairment	328		333
Loans collectively evaluated for impairment	231,341		188,585
Gross loans receivable after deferred loan costs and premiums	231,669		188,918
Commercial real estate
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	61		71
Total ending allowance balance	61	65	71	77	75	215
Loans:
Loans collectively evaluated for impairment	6,007		6,096
Gross loans receivable after deferred loan costs and premiums	6,007		6,096
Church
Ending allowance balance attributable to loans:
Individually evaluated for impairment	415		479
Collectively evaluated for impairment	510		602
Total ending allowance balance	925	1,005	1,081	1,104	1,250	1,337
Loans:
Loans individually evaluated for impairment	7,554		8,280
Loans collectively evaluated for impairment	21,775		22,232
Gross loans receivable after deferred loan costs and premiums	29,329		30,512
Construction
Ending allowance balance attributable to loans:
Collectively evaluated for impairment	18		17
Total ending allowance balance	18	11	17	9	9	8
Loans:
Loans collectively evaluated for impairment	1,761		1,671
Gross loans receivable after deferred loan costs and premiums	1,761		1,671
Commercial - other
Ending allowance balance attributable to loans:
Individually evaluated for impairment	4		5
Collectively evaluated for impairment	2		1
Total ending allowance balance	6	$ 6	6	$ 17	16	$ 17
Loans:
Loans individually evaluated for impairment	64		65
Loans collectively evaluated for impairment	137		127
Gross loans receivable after deferred loan costs and premiums	201		192
Consumer
Ending allowance balance attributable to loans:
Total ending allowance balance					$ 1
Loans:
Loans collectively evaluated for impairment	7		7
Gross loans receivable after deferred loan costs and premiums	$ 7		$ 7