Debt instrument, expiration of initial interest only period.

No definition available.

Name:	alna_DebtInstrumentExpirationOfInitialInterestOnlyPeriod
Namespace Prefix:	alna_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument interest only payment period.

+ References

No definition available.

+ Details

Name:	alna_DebtInstrumentInterestOnlyPaymentPeriod
Namespace Prefix:	alna_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument repayment, number of monthly payments.

+ References

No definition available.

+ Details

Name:	alna_DebtInstrumentRepaymentNumberOfMonthlyPayments
Namespace Prefix:	alna_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Gross proceeds from issuance of common stock.

+ References

No definition available.

+ Details

Name:	alna_GrossProceedsFromIssuanceOfCommonStock
Namespace Prefix:	alna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Minimum gross proceeds from debt threshold for success fee.

+ References

No definition available.

+ Details

Name:	alna_MinimumGrossProceedsFromDebtThresholdForSuccessFee
Namespace Prefix:	alna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Success fee payable.

+ References

No definition available.

+ Details

Name:	alna_SuccessFeePayable
Namespace Prefix:	alna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentFrequencyOfPeriodicPayment
Namespace Prefix:	us-gaap_
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

No definition available.

+ Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

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

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3291-108585

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=alna_LoanAndSecurityAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=alna_PacificWesternBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=alna_DirectPublicOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=alna_MarketOfferingMember
Namespace Prefix:
Data Type:	na
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Period Type:

Loan and Security Agreement - Additional Information (Details) - USD ($)				1 Months Ended		12 Months Ended
	Sep. 29, 2020	Jun. 05, 2020	Jun. 29, 2018	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Loan agreement, advanced amount							$ 10,000,000
Loan and Security Agreement \| PWB
Debt Instrument [Line Items]
Loan agreement, maximum borrowing capacity			$ 12,000,000.0
Loan agreement, advanced amount			10,000,000.0
Loan agreement, remaining borrowing capacity			$ 2,000,000.0
Loan agreement, interest rate above prime rate			5.00%
Loan agreement, term			48 months
Loan agreement, interest only payment period			18 months
Expiration of interest only period			Dec. 31, 2019
Loan agreement, number of monthly payments			30 months
Loan agreement, frequency of payments						monthly
Aggregate gross proceeds for success fee to be paid			$ 25,000,000
Success fee payable			$ 300,000
Repayment of outstanding principal balance	$ 7,000,000.0
Direct Offering
Debt Instrument [Line Items]
Gross proceeds from issuance of common stock		$ 15,000,000.0			$ 10,000,000.0
At-the-Market Offering
Debt Instrument [Line Items]
Gross proceeds from issuance of common stock				$ 2,700,000