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Commitment and Contingencies - Addtional Information (Details)	Mar. 31, 2026 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Indemnification agreement liability	$ 0

X

- Definition

Indemnification agreement liability.

+ References

No definition available.

+ Details

Name:	alec_IndemnificationAgreementLiability
Namespace Prefix:	alec_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

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