Number of convertible preferred shares issued for each share of convertible preferred stock that is converted.

No definition available.

Name:	alms_ConvertiblePreferredStockNumberOfSharesIssuedUponConversion
Namespace Prefix:	alms_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of derivative liability reclassified into temporary equity.

+ References

No definition available.

+ Details

Name:	alms_DerivativeLiabilityAmountReclassifiedToTemporaryEquity
Namespace Prefix:	alms_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Market value / fair value of freestanding financial instruments held by the company.

+ References

No definition available.

+ Details

Name:	alms_FairValueOfFreestandingFinancialInstruments
Namespace Prefix:	alms_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of freestanding financial instruments held by the company.

+ References

No definition available.

+ Details

Name:	alms_NumberOfFreestandingFinancialInstruments
Namespace Prefix:	alms_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Redeemable convertible preferred stock recognized call option

+ References

No definition available.

+ Details

Name:	alms_RedeemableConvertiblePreferredStockCallOption
Namespace Prefix:	alms_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of shares issued as redeemable preferred stock during the period.

+ References

No definition available.

+ Details

Name:	alms_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	alms_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares issued for each share of convertible preferred stock that is converted.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(27))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-3

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-16

+ Details

Name:	us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow for cost incurred directly with the issuance of an equity security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-15

+ Details

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

- Definition

The cash inflow from issuance of callable preferred stock which is identified as being convertible to another type of financial security at the option of the issuer or the holder.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 14
-Subparagraph (a)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-14

+ Details

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

- Definition

Per share or per unit amount of equity securities issued.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesIssuedPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
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_TemporaryEquityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementClassOfStockAxis=alms_SeriesB2RedeemableConvertiblePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=alms_SeriesB2aRedeemableConvertiblePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=alms_SeriesCRedeemableConvertiblePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=alms_SeriesC1RedeemableConvertiblePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=alms_SeriesB2B2aRedeemableConvertiblePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=alms_VotingCommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Redeemable Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended				12 Months Ended
	May 31, 2024 USD ($) $ / shares shares	Mar. 31, 2024 USD ($) instrument $ / shares shares	Oct. 31, 2023 USD ($) $ / shares shares	May 31, 2023 USD ($) $ / shares shares	Dec. 31, 2023 USD ($)	Jul. 31, 2023 shares
Redeemable Convertible Preferred Stock
Offering cost					$ 485
Derivative liability				$ 2,100
Derivative liability reclassified to temporary equity			$ 2,200
Number of Freestanding Financial Instruments \| instrument		2
Fair value of freestanding instrument		$ 8,900
Series B-2 redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Shares issued \| shares			4,221,170	10,722,340
Proceeds from issuance of shares			$ 21,100	$ 53,600
Issue price per share \| $ / shares			$ 5	$ 5
Number of convertible preferred shares issued \| shares						1,277,660
Series B-2 redeemable convertible preferred stock \| Maximum
Redeemable Convertible Preferred Stock
Offering cost			$ 100
Series B-2A redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Shares issued \| shares			1,778,830	1,277,660
Proceeds from issuance of shares			$ 8,900	$ 6,400
Issue price per share \| $ / shares			$ 5.00	$ 5.00
Series C redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Shares issued \| shares	41,264,892	41,264,891
Proceeds from issuance of shares	$ 129,500	$ 129,500
Offering cost	$ 200	$ 400
Issue price per share \| $ / shares	$ 3.13826	$ 3.13826
Derivative liability reclassified to temporary equity	$ 14,300
Number of Freestanding Financial Instruments \| instrument		2
Series C-1 redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Issue price per share \| $ / shares		$ 4
Series B-2, B-2A redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Offering cost				$ 200
Voting common stock
Redeemable Convertible Preferred Stock
Number of shares issued upon conversion \| shares		0.1