Loans Receivable and Allowance for Loan and Lease Losses Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	$ 4,792	$ 5,126	$ 5,126	$ 5,060
Charge-offs	(503)	(70)	(1,093)	(211)
Recoveries	845	8	1,047	91
Provision for loan losses	(332)	6	(278)	130
Allowance for loan losses - Ending Balance	4,802	5,070	4,802	5,070
Allowance for Loan Losses, Collectively Evaluated for Impairment	4,609		4,609		$ 4,811
Allowance for Loan Losses, Individually Evaluated for Impairment	193		193		315
Loans, gross	427,407		427,407		477,753
Loans Receivable, Collectively Evaluated for Impairment	415,200		415,200		464,716
Loans Receivable, Individually Evaluated for Impairment	12,207		12,207		13,037
One-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	1,481	1,179	1,210	1,663
Charge-offs	(6)	0	(151)	(93)
Recoveries	186	0	186	0
Provision for loan losses	(198)	(52)	218	(443)
Allowance for loan losses - Ending Balance	1,463	1,127	1,463	1,127
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,288		1,288		1,065
Allowance for Loan Losses, Individually Evaluated for Impairment	175		175		145
Loans, gross	111,776		111,776		123,092
Loans Receivable, Collectively Evaluated for Impairment	106,333		106,333		116,588
Loans Receivable, Individually Evaluated for Impairment	5,443		5,443		6,504
Multifamily
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	939	1,369	1,819	1,213
Charge-offs	0	(36)	(100)	(42)
Recoveries	0	0	158	0
Provision for loan losses	(65)	(25)	(1,003)	137
Allowance for loan losses - Ending Balance	874	1,308	874	1,308
Allowance for Loan Losses, Collectively Evaluated for Impairment	874		874		1,744
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0		75
Loans, gross	87,705		87,705		104,865
Loans Receivable, Collectively Evaluated for Impairment	84,997		84,997		103,160
Loans Receivable, Individually Evaluated for Impairment	2,708		2,708		1,705
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	702	1,692	1,052	1,496
Charge-offs	0	0	0	0
Recoveries	0	5	0	15
Provision for loan losses	36	(25)	(314)	161
Allowance for loan losses - Ending Balance	738	1,672	738	1,672
Allowance for Loan Losses, Collectively Evaluated for Impairment	738		738		1,052
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0		0
Loans, gross	124,352		124,352		142,304
Loans Receivable, Collectively Evaluated for Impairment	123,870		123,870		140,765
Loans Receivable, Individually Evaluated for Impairment	482		482		1,539
Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	0	0	0	106
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	0	0	0	(106)
Allowance for loan losses - Ending Balance	0	0	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	0		0		0
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0		0
Loans, gross	0		0		0
Loans Receivable, Collectively Evaluated for Impairment	0		0		0
Loans Receivable, Individually Evaluated for Impairment	0		0		0
Business
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	1,530	832	1,003	573
Charge-offs	(490)	(27)	(830)	(47)
Recoveries	658	3	667	72
Provision for loan losses	(320)	(31)	538	179
Allowance for loan losses - Ending Balance	1,378	777	1,378	777
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,360		1,360		908
Allowance for Loan Losses, Individually Evaluated for Impairment	18		18		95
Loans, gross	99,118		99,118		102,203
Loans Receivable, Collectively Evaluated for Impairment	95,544		95,544		98,914
Loans Receivable, Individually Evaluated for Impairment	3,574		3,574		3,289
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	140	20	18	9
Charge-offs	(7)	(7)	(12)	(29)
Recoveries	1	0	36	4
Provision for loan losses	(12)	8	80	37
Allowance for loan losses - Ending Balance	122	21	122	21
Allowance for Loan Losses, Collectively Evaluated for Impairment	122		122		18
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0		0
Loans, gross	4,456		4,456		5,289
Loans Receivable, Collectively Evaluated for Impairment	4,456		4,456		5,289
Loans Receivable, Individually Evaluated for Impairment	0		0		0
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses - Beginning Balance	0	34	24	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	227	131	203	165
Allowance for loan losses - Ending Balance	227	$ 165	227	$ 165
Allowance for Loan Losses, Collectively Evaluated for Impairment	227		227		24
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0		0
Loans, gross	0		0		0
Loans Receivable, Collectively Evaluated for Impairment	0		0		0
Loans Receivable, Individually Evaluated for Impairment	$ 0		$ 0		$ 0

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: