Summary of significant accounting policies - Summary of Estimated Useful Life of Asset (Detail)	12 Months Ended
Dec. 31, 2024
Property Plant And Equipment [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeTermOfLeaseMember
Lab Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful life of asset	3 years
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful life of asset	3 years
Vehicles [Member]
Property Plant And Equipment [Line Items]
Estimated useful life of asset	4 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Estimated useful life of asset	Shorter of the useful life orremaining lease term
Minimum [Member] \| Furniture and Office Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful life of asset	3 years
Maximum [Member] \| Furniture and Office Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated useful life of asset	8 years

Property plant and equipment estimated useful lives.

No definition available.

Name:	algs_PropertyPlantAndEquipmentEstimatedUsefulLives1
Namespace Prefix:	algs_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-7A

+ Details

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

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Indicates description of term of useful life for property, plant, and equipment when not stated as numeric value.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482190/360-10-35-3

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLifeDescriptionOfTermExtensibleEnumeration
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=algs_LabEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ComputerEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_VehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LeaseholdImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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