Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

Name:	us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

Name:	us-gaap_ProvisionForLoanAndLeaseLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=srt_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_UnallocatedFinancingReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans Receivable, Net - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				$ 5,060		$ 5,232			$ 5,060
Charge-offs									(314)	$ (529)
Recoveries									245	328
Provision for loan losses	$ 5	$ 6	$ 4	120	$ 521	(128)	$ (160)	$ (204)	135	29
Allowance for loan losses - Ending Balance	5,126				5,060		5,232		5,126	5,060
Allowance for Loan Losses, Collectively Evaluated for Impairment	4,811				4,699				4,811	4,699
Allowance for Loan Losses, Individually Evaluated for Impairment	315				361				315	361
Loans, gross	477,753				545,552				477,753	545,552
Loans Receivable, Collectively Evaluated for Impairment	464,716				530,859				464,716	530,859
Loans Receivable, Individually Evaluated for Impairment	13,037				14,693				13,037	14,693
One-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				1,663		1,697			1,663
Charge-offs									(96)	(106)
Recoveries									0	0
Provision for loan losses									(357)	72
Allowance for loan losses - Ending Balance	1,210				1,663		1,697		1,210	1,663
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,065				1,357				1,065	1,357
Allowance for Loan Losses, Individually Evaluated for Impairment	145				306				145	306
Loans, gross	123,092				134,927				123,092	134,927
Loans Receivable, Collectively Evaluated for Impairment	116,588				129,420				116,588	129,420
Loans Receivable, Individually Evaluated for Impairment	6,504				5,507				6,504	5,507
Multifamily
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				1,213		622			1,213
Charge-offs									(104)	(338)
Recoveries									131	0
Provision for loan losses									579	929
Allowance for loan losses - Ending Balance	1,819				1,213		622		1,819	1,213
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,744				1,207				1,744	1,207
Allowance for Loan Losses, Individually Evaluated for Impairment	75				6				75	6
Loans, gross	104,865				88,750				104,865	88,750
Loans Receivable, Collectively Evaluated for Impairment	103,160				87,148				103,160	87,148
Loans Receivable, Individually Evaluated for Impairment	1,705				1,602				1,705	1,602
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				1,496		1,808			1,496
Charge-offs									0	0
Recoveries									20	20
Provision for loan losses									(464)	(332)
Allowance for loan losses - Ending Balance	1,052				1,496		1,808		1,052	1,496
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,052				1,490				1,052	1,490
Allowance for Loan Losses, Individually Evaluated for Impairment	0				6				0	6
Loans, gross	142,304				242,818				142,304	242,818
Loans Receivable, Collectively Evaluated for Impairment	140,765				239,323				140,765	239,323
Loans Receivable, Individually Evaluated for Impairment	1,539				3,495				1,539	3,495
Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				106		62			106
Charge-offs									0	0
Recoveries									0	0
Provision for loan losses									(106)	44
Allowance for loan losses - Ending Balance	0				106		62		0	106
Allowance for Loan Losses, Collectively Evaluated for Impairment	0				106				0	106
Allowance for Loan Losses, Individually Evaluated for Impairment	0				0				0	0
Loans, gross	0				4,949				0	4,949
Loans Receivable, Collectively Evaluated for Impairment	0				4,949				0	4,949
Loans Receivable, Individually Evaluated for Impairment	0				0				0	0
Business
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				573		1,022			573
Charge-offs									(81)	0
Recoveries									87	304
Provision for loan losses									424	(753)
Allowance for loan losses - Ending Balance	1,003				573		1,022		1,003	573
Allowance for Loan Losses, Collectively Evaluated for Impairment	908				532				908	532
Allowance for Loan Losses, Individually Evaluated for Impairment	95				41				95	41
Loans, gross	102,203				65,114				102,203	65,114
Loans Receivable, Collectively Evaluated for Impairment	98,914				61,027				98,914	61,027
Loans Receivable, Individually Evaluated for Impairment	3,289				4,087				3,289	4,087
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				9		$ 21			9
Charge-offs									(33)	(85)
Recoveries									7	4
Provision for loan losses									35	69
Allowance for loan losses - Ending Balance	18				9		$ 21		18	9
Allowance for Loan Losses, Collectively Evaluated for Impairment	18				7				18	7
Allowance for Loan Losses, Individually Evaluated for Impairment	0				2				0	2
Loans, gross	5,289				8,994				5,289	8,994
Loans Receivable, Collectively Evaluated for Impairment	5,289				8,992				5,289	8,992
Loans Receivable, Individually Evaluated for Impairment	0				2				0	2
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance				$ 0					0
Charge-offs									0
Recoveries									0
Provision for loan losses									24
Allowance for loan losses - Ending Balance	24				$ 0				24	$ 0
Allowance for Loan Losses, Collectively Evaluated for Impairment	24								24
Allowance for Loan Losses, Individually Evaluated for Impairment	0								0
Loans, gross	0								0
Loans Receivable, Collectively Evaluated for Impairment	0								0
Loans Receivable, Individually Evaluated for Impairment	$ 0								$ 0