Collaboration and License Agreements - Additional Information (Details)		1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2019 shares	Apr. 30, 2019 USD ($) Product	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Obligation	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			$ 1,746,000	$ 650,000	$ 4,645,000	$ 874,000
Lilly Note | Series C Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Conversion of convertible note payable to preferred stock | shares	4,576,342
Research Collaboration and License Agreement with Eli Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fees received		$ 20,000,000
License agreement expiry period		10 years
Number of performance obligation | Obligation					1
Period for expects performance obligation					5 years
Revenue recognized			1,700,000	$ 700,000	$ 4,600,000	$ 900,000
Deferred revenue			$ 16,820,000		$ 16,820,000		$ 18,940,000
Research Collaboration and License Agreement with Eli Lilly | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Rights to antibody oligonucleotide conjugates for messengers RNA targets. | Product		6
Development milestone payment eligible to receive per target		$ 60,000,000
Regulatory milestone payment eligible to receive per target		140,000,000
Commercialization milestone payment eligible to receive		$ 205,000,000