Name:	hmst_DerivativeAssetFairValueAmountOffsetAgainstOtherDerivatives
Namespace Prefix:	hmst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The amount as of the balance sheet date of the fair value of derivative liabilities that in accordance with the entity's accounting policy were offset against other derivative contracts under a master netting arrangement.

No definition available.

Name:	hmst_DerivativeLiabilityFairValueAmountOffsetAgainstOtherDerivatives
Namespace Prefix:	hmst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480463/815-10-45-5

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-SubTopic 20
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

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

- References

No definition available.

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

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-22

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-7

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-SubTopic 20
-Topic 860
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481326/860-20-50-4D

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

Fair value, after effect of master netting arrangement and deduction of obligation to return financial collateral not offset and financial instrument subject to master netting arrangement not offset, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and contract can be net settled by means outside contract or delivery of asset. Includes derivative not subject to master netting arrangement or similar agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 55
-Paragraph 13
-SubTopic 20
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-13

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-8

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

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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

Fair value, after effect of master netting arrangement and deduction of obligation to return financial collateral not offset and financial instrument subject to master netting arrangement not offset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and contract can be net settled by means outside contract or delivery of asset. Includes derivative not subject to master netting arrangement or similar agreement.

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

- References

No definition available.

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

Nominal or face amount used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

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.

No definition available.

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

Name:	us-gaap_FairValueConcentrationOfRiskDisclosureItemsAxis=us-gaap_FairValueConcentrationOfCreditRiskMasterNettingArrangementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForwardContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_FutureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: