Collaboration and License Agreements - Additional Information (Details)		1 Months Ended				12 Months Ended
	Dec. 22, 2018 USD ($) Target	Sep. 30, 2021 USD ($)	Aug. 31, 2021	May 31, 2021 USD ($)	Dec. 31, 2018 USD ($) Target Protein	Dec. 31, 2021 USD ($) Target Performanceobligation TargetProtein	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue						$ 34,363,000	$ 17,570,000	$ 11,948,000
Transaction price allocated to performance obligation						$ 65,322,000
Restated Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of potential targets | Target	5
Additional upfront consideration received	$ 40,000,000.0
Annual research plan payments receivables	$ 1,000,000.0
Annual research plan payments periods	3 years
Collaboration description						The collaboration is managed by a joint research committee. The Company has control over the committee and may terminate the Roche Agreement on a target-by-target or product-by-product basis under several scenarios, upon at least 90 days’ prior written notice.
Restated Roche Agreement | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise fees	$ 7,000,000.0
Restated Roche Agreement | Minimum | Research, Development and Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive	260,000,000
Restated Roche Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise fees	20,000,000.0
Restated Roche Agreement | Maximum | Research, Development and Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive	275,000,000.0
Restated Roche Agreement | Maximum | One-Time Sales-Based Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive	150,000,000.0
Restated Roche Agreement | Lead Series Identification Achievement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fees	2,000,000.0
Restated Roche Agreement | Good Laboratory Practice (“GLP”) Toxicology (“Tox”) Study Phase
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fees	$ 3,000,000.0
Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue						$ 65,300,000
Roche Agreement | Research and Development Target and Option Right
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue						$ 12,600,000
Biogen License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets | Target						5
Agreement date					2018-12
Research agreement, period					54 months
Additional payment on extension of contract					$ 62,500,000
Nonrefundable upfront payment						$ 45,000,000.0
Number of performance obligation | Performanceobligation						1
Number of additional targets | Target						2
Biogen License Agreement | Research and Development Services
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue						$ 55,000,000.0
Transaction price allocated to performance obligation						30,600,000
Milestone earned						$ 6,000,000.0	$ 4,000,000.0
Biogen License Agreement | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Written notice period for termination of agreement						90 days
Biogen License Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targeted protein degradation | Protein					5
Additional targets for development | Target					5
Biogen License Agreement | Maximum | One-Time Sales-Based Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received						$ 26,000,000.0
Biogen License Agreement | Maximum | Research And Development Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received						$ 35,000,000.0
Calico License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets | Target						5
Number of performance obligation | Performanceobligation						1
Research term						5 years
Upfront payment						$ 5,000,000.0
Annual Payments						$ 5,000,000.0
Research extend term			1 year
Amount payable for extend research term option		$ 1,000,000.0
Initial contractual term on straight line basis						5 years
Contractual term						6 years
Additional transaction price allocated to performance obligation				$ 1,000,000.0
Calico License Agreement | Research and Development Services
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price recognized as collaboration revenue						$ 13,000,000.0
Transaction price allocated to performance obligation						$ 2,700,000
Calico License Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of target proteins | TargetProtein						5
Calico License Agreement | Maximum | One-Time Sales-Based Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received						$ 65,000,000.0
Calico License Agreement | Maximum | Potential Research, Development and Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received						132,000,000.0
Calico License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated to performance obligation						$ 63,800,000