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

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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:	num: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=75038535&loc=d3e64711-112823

+ Details

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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=121586364&loc=d3e3255-108585

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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_MarketOfferingMember
Namespace Prefix:
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Loan and Security Agreement - Additional Information (Details) - USD ($)					6 Months Ended
	Jun. 05, 2020	Dec. 31, 2019	Jun. 30, 2019	Jun. 29, 2018	Jun. 30, 2020
Direct Offering
Debt Instrument [Line Items]
Gross proceeds from issuance of common stock	$ 15,000,000
Loan Agreement \| PWB
Debt Instrument [Line Items]
Loan agreement, maximum borrowing capacity				$ 12,000,000
Loan agreement, advanced amount				10,000,000
Loan agreement, remaining borrowing capacity				$ 2,000,000
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
Loan Agreement \| PWB \| Direct Offering
Debt Instrument [Line Items]
Gross proceeds from issuance of common stock	$ 15,000,000		$ 10,000,000
Loan Agreement \| PWB \| At-the-Market Offering
Debt Instrument [Line Items]
Gross proceeds from issuance of common stock		$ 2,700,000