LOANS AND CREDIT QUALITY - Activity in Allowance for Credit Losses by Loan Portfolio (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Allowance for credit losses by loan portfolio
Beginning balance	$ 39,634	$ 39,677	$ 38,743	$ 40,500	$ 40,500
Charge-offs	(47)	(126)	(108)	(1,231)	(3,141)
Provision	59	62	123	102
Provision	6,160	128	7,048	370
Ending balance	45,806	39,741	45,806	39,741	38,743
Commercial and industrial loans \| Real Estate Sector
Allowance for credit losses by loan portfolio
Beginning balance	21,330	28,900	24,484	27,912	27,912
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	5,989	(2,302)	2,835	(1,314)
Ending balance	27,319	26,598	27,319	26,598	24,484
Commercial and industrial loans \| Commercial and Industrial Sector
Allowance for credit losses by loan portfolio
Beginning balance	11,246	3,482	7,462	3,849	3,849
Charge-offs	(20)	(39)	(41)	(1,120)
Provision	25	39	50	40
Provision	509	2,844	4,289	3,557
Ending balance	11,760	6,326	11,760	6,326	7,462
Commercial and industrial loans \| Non-owner occupied CRE
Allowance for credit losses by loan portfolio
Beginning balance	1,658	2,131	1,739	2,610	2,610
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	133	(354)	52	(833)
Ending balance	1,791	1,777	1,791	1,777	1,739
Commercial and industrial loans \| Multifamily
Allowance for credit losses by loan portfolio
Beginning balance	13,287	18,947	14,909	13,093	13,093
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	5,661	(1,877)	4,039	3,977
Ending balance	18,948	17,070	18,948	17,070	14,909
Commercial and industrial loans \| Multifamily construction
Allowance for credit losses by loan portfolio
Beginning balance	468	1,621	849	3,983	3,983
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	691	350	310	(2,012)
Ending balance	1,159	1,971	1,159	1,971	849
Commercial and industrial loans \| Construction/land development
Allowance for credit losses by loan portfolio
Beginning balance	73	188	66	189	189
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	(2)	(153)	5	(154)
Ending balance	71	35	71	35	66
Commercial and industrial loans \| Single family construction
Allowance for credit losses by loan portfolio
Beginning balance	5,704	5,578	6,737	7,365	7,365
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	(504)	(133)	(1,537)	(1,920)
Ending balance	5,200	5,445	5,200	5,445	6,737
Commercial and industrial loans \| Single family construction to permanent
Allowance for credit losses by loan portfolio
Beginning balance	140	435	184	672	672
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	10	(135)	(34)	(372)
Ending balance	150	300	150	300	184
Commercial and industrial loans \| Owner occupied CRE
Allowance for credit losses by loan portfolio
Beginning balance	598	836	576	899	899
Charge-offs	0	0	0	0
Provision	0	0	0	0
Provision	12	(105)	34	(168)
Ending balance	610	731	610	731	576
Commercial and industrial loans \| Commercial business
Allowance for credit losses by loan portfolio
Beginning balance	10,648	2,646	6,886	2,950	2,950
Charge-offs	(20)	(39)	(41)	(1,120)	(2,963)
Provision	25	39	50	40
Provision	497	2,949	4,255	3,725
Ending balance	11,150	5,595	11,150	5,595	6,886
Consumer loans
Allowance for credit losses by loan portfolio
Beginning balance	7,058	7,295	6,797	8,739	8,739
Charge-offs	(27)	(87)	(67)	(111)
Provision	34	23	73	62
Provision	(338)	(414)	(76)	(1,873)
Ending balance	6,727	6,817	6,727	6,817	6,797
Consumer loans \| Single family
Allowance for credit losses by loan portfolio
Beginning balance	3,702	4,273	3,610	5,287	5,287
Charge-offs	0	0	0	0
Provision	1	1	3	3
Provision	(101)	(430)	(11)	(1,446)
Ending balance	3,602	3,844	3,602	3,844	3,610
Consumer loans \| Home equity and other
Allowance for credit losses by loan portfolio
Beginning balance	3,356	3,022	3,187	3,452	3,452
Charge-offs	(27)	(87)	(67)	(111)	(178)
Provision	33	22	70	59
Provision	(237)	16	(65)	(427)
Ending balance	$ 3,125	$ 2,973	$ 3,125	$ 2,973	$ 3,187

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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

- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

+ Details

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

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

+ Details

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

- Details

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

- Details

Name:	us-gaap_EquitySecuritiesByIndustryAxis=us-gaap_RealEstateSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquitySecuritiesByIndustryAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_NonOwnerOccupiedCommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_MultifamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_MultifamilyConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_CommercialRealEstateConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_SingleFamilyConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_SingleFamilyConstructionToPermanentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_OwnerOccupiedCommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialLoanMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=hmst_HomeEquityLineOfCreditAdjustedForCreditAnalysisMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: