Cashless exercise of warrants.

No definition available.

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- Definition

Class of warrant exercisable common stock warrant exercise price.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Class of warrant exercisable for common stock.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Class of warrant number of securities called by each warrant to purchase common stock.

+ References

No definition available.

+ Details

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- Definition

Class of warrant number of securities called by each warrant to purchase convertible preferred stock.

+ References

No definition available.

+ Details

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- Definition

Class of warrant or right term.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt instrument final payment percentage.

+ References

No definition available.

+ Details

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Namespace Prefix:	rna_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument final payments.

+ References

No definition available.

+ Details

Name:	rna_DebtInstrumentFinalPayments
Namespace Prefix:	rna_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Debt instrument frequency of periodic payment interest

+ References

No definition available.

+ Details

Name:	rna_DebtInstrumentFrequencyOfPeriodicPaymentInterest
Namespace Prefix:	rna_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument frequency of periodic payment principal.

+ References

No definition available.

+ Details

Name:	rna_DebtInstrumentFrequencyOfPeriodicPaymentPrincipal
Namespace Prefix:	rna_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of monthly installments of principal.

+ References

No definition available.

+ Details

Name:	rna_NumberOfMonthlyInstallmentsOfPrincipal
Namespace Prefix:	rna_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Payment of final payment and accrued interest.

+ References

No definition available.

+ Details

Name:	rna_PaymentOfFinalPaymentAndAccruedInterest
Namespace Prefix:	rna_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

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Data Type:	num:perShareItemType
Balance Type:	na
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

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from the issuance of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

+ 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

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal 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 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

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Balance Type:	credit
Period Type:	duration

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- Details

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- Details

Name:	srt_RangeAxis=srt_MaximumMember
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- Details

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Debt - Additional Information (Details)		1 Months Ended			9 Months Ended
Debt - Additional Information (Details)	Jun. 17, 2020 shares	Jun. 30, 2020 USD ($) $ / shares shares	Aug. 31, 2018 USD ($)	Jun. 30, 2017 USD ($) Installment $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)
Debt Instrument [Line Items]
Repayment of existing loan					$ 4,683,000	$ 2,100,000
Proceeds from notes					$ 0	$ 19,451,000
Common Stock
Debt Instrument [Line Items]
Warrant exercisable \| shares		7,809
Exercise price of warrant \| $ / shares		$ 4.77
Cashless exercise of warrants \| shares	15,833
SVB
Debt Instrument [Line Items]
Repayment of existing loan				$ 4,100,000
Debt instrument final payments				$ 400,000
SVB \| Convertible Notes
Debt Instrument [Line Items]
Proceeds from notes			$ 3,000,000
SVB \| Term C Loan \| Common Stock
Debt Instrument [Line Items]
Warrant term					7 years
Exercise price of warrant \| $ / shares				$ 0.53
SVB \| Term C Loan \| Common Stock \| Maximum
Debt Instrument [Line Items]
Warrant to purchase common stock \| shares				9,442
SVB \| Term A And Term B Loans \| Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Exercise price of warrant \| $ / shares					$ 2.2615
Warrant term					10 years
SVB \| Term A And Term B Loans \| Series A Convertible Preferred Stock \| Maximum
Debt Instrument [Line Items]
Warrant to purchase convertible preferred stock \| shares					16,474
SVB \| LSA Amendment
Debt Instrument [Line Items]
Loan facility maximum borrowing capacity				$ 7,000,000
SVB \| LSA Amendment \| Term C Loan
Debt Instrument [Line Items]
Face amount of loans				5,000,000
Debt instrument final payments				$ 300,000
Maturity date				Jun. 01, 2021
Basis spread on variable rate				0.20%
Frequency of periodic payment principal					36 equal monthly
Number of equal monthly installments of principal \| Installment				36
Frequency of periodic payment interest					monthly
Debt instrument final payment percentage				6.50%
SVB \| LSA Amendment \| Term D Loan
Debt Instrument [Line Items]
Face amount of loans			2,000,000
SVB \| LSA Second Amendment \| Term D Loan
Debt Instrument [Line Items]
Debt instrument final payments			$ 100,000
Debt instrument final payment percentage			6.50%
Proceeds from issuance of long-term debt			$ 2,000,000
SVB \| LSA \| Term C And D Loans
Debt Instrument [Line Items]
Loans prepaid amount		$ 2,800,000
Payment of final payment and accrued interest		$ 500,000