0001564590-21-054522 | 10-Q | XBRL Viewer

Supplemental Balance Sheet Information - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Supplemental Balance Sheet Information Disclosures [Abstract]
Tax incentive refund	$ 2,662	$ 2,558
Prepaid research and development expenses	4,560	3,145
Prepaid compensation benefits	$ 706	$ 609

Label	Element	Value
Undesignated Preferred Stock	avro_UndesignatedPreferredStock	10,000,000
Undesignated Preferred Stock	avro_UndesignatedPreferredStock	10,000,000
Line Of Credit Facility Additional Discretionary	avro_LineOfCreditFacilityAdditionalDiscretionary	$ 15,000,000.0
Accrued Research And Development Expense Current	avro_AccruedResearchAndDevelopmentExpenseCurrent	11,233,000
Accrued Research And Development Expense Current	avro_AccruedResearchAndDevelopmentExpenseCurrent	5,847,000
Fair Value Input Amount Transfer Between Levels	avro_FairValueInputAmountTransferBetweenLevels	0
Deferred Rent Expense	avro_DeferredRentExpense	(159,000)
Deferred Rent Expense	avro_DeferredRentExpense	$ (151,000)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited And Expirations In Period	avro_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedAndExpirationsInPeriod	63,342
Undesignated Shares Of Preferred Stock Outstanding	avro_UndesignatedSharesOfPreferredStockOutstanding	0
Undesignated Shares Of Preferred Stock Outstanding	avro_UndesignatedSharesOfPreferredStockOutstanding	0

License Agreements - Additional Information (Detail) £ in Thousands, $ in Thousands							3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2020 GBP (£)	Oct. 02, 2017 USD ($)	Aug. 31, 2017 USD ($)	Jan. 27, 2016 USD ($)	Jan. 27, 2016 CAD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Nov. 17, 2016 USD ($)	Jan. 27, 2016 CAD ($)
License Agreement [Line Items]
Upfront license fee			$ 1,000,000	$ 500,000		$ 264					$ 8,000,000
Milestone payments payable	$ 80,000,000		$ 16,000,000	$ 13,000,000	$ 2,000,000			$ 80,000,000		$ 80,000,000		$ 550,000	$ 19,275
Milestone payment paid	2,000,000
Milestone payment due	$ 4,000,000
Agreement expiration period									15 years
Agreement expiration description									upon the later of 15 years from the effective date or the expiration of the last valid claim of the licensed patent
Research and development expense		£ 9,275					$ 102,000	65,000	$ 175,000	174,000
Collaborative agreement expenses							1,000,000.0	0	1,800,000	0
Option fee						20
Milestone fees							0	0	0	0
Annual maintenance fees						$ 50
Payments upon closing of an initial public offering					$ 2,000,000
Expenses related to license							$ 0	$ 0	$ 0	$ 0

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