Collaboration and License Agreements - Additional Information (Details)		1 Months Ended			3 Months Ended		9 Months Ended
	Dec. 22, 2018 USD ($) Target	Apr. 30, 2019 USD ($)	Dec. 31, 2018 USD ($) Protein Target	Mar. 31, 2016 USD ($) Protein Reimbursement	Sep. 30, 2020 USD ($) Target Exchange Performanceobligation TargetProtein	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Target Exchange MaterialRight Performanceobligation TargetProtein	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)
Original Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment							$ 40,000,000
Expected research plan funding payments							13,500,000
Remaining deferred revenue					$ 6,400,000		$ 6,400,000
Original Roche Agreement | Roche JRC | Research and Development License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Nonrefundable upfront payment and additional fees				$ 15,000,000
Estimated period to perform research and development				42 months
Original Roche Agreement | Roche JRC | Research, Development and Commercial Milestone Payments | Research and Development License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive				$ 277,000,000
Original Roche Agreement | Maximum | Roche
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targeted protein degradation | Protein				10
Original Roche Agreement | Maximum | Roche JRC | Research and Development License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of reimbursements in full-time equivalents | Reimbursement				5
Original Roche Agreement | Maximum | Roche JRC | One-Time Sales-Based Payments | Research and Development License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive				$ 150,000,000
Restated Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of potential targets | Target	6				6		6
Number of target nominated as of the execution of the Restated Roche Agreement | Target	3
Number of target not nominated as of the execution of the Restated Roche Agreement | Target	3
Additional upfront consideration received	$ 40,000,000
Annual research plan payments receivables	1,000,000
Collaboration description							The Company has control over the committee and may terminate the Restated Roche Agreement on a target-by-target or product-by-product basis under several scenarios, upon at least 90 days’ prior written notice.
Number of initial targets | Target					3		3
Number of additional targets | Target							3
Number of targets | Target					6		6
Number of exchanges | Exchange					6		6
Number of additional targets | Target					3		3
Number of performance obligation | Performanceobligation					12		12
Restated Roche Agreement | Lead Series Identification Achievement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fees	2,000,000
Restated Roche Agreement | Good Laboratory Practice (“GLP”) Toxicology (“Tox”) Study Phase
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fees	3,000,000
Restated Roche Agreement | Progressed Through Clinical Trials
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise fees	20,000,000
Restated Roche Agreement | Option to License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of material rights | MaterialRight							3
Restated Roche Agreement | Option to Initiate Research Plan
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of additional targets | Target							3
Number of material rights | MaterialRight							3
Restated Roche Agreement | Research Services Performance Obligations
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of performance obligation | Performanceobligation					3		3
Restated Roche Agreement | Commercial License for Six Targets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets | Target					6		6
Number of performance obligation | Performanceobligation					6		6
Restated Roche Agreement | Research Services for Uninitiated Three Targets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of targets | Target					3		3
Number of performance obligation | Performanceobligation					3		3
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
Restated Roche Agreement | Maximum | One-Time Sales-Based Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount eligible to receive	150,000,000
Restated Roche Agreement | Maximum | Progressed Through Clinical Trials
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise fees	12,000,000
Restated Roche Agreement | Minimum | Progressed Through Clinical Trials
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise fees	$ 7,000,000
Restated Roche Agreement Accounting
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment							$ 40,000,000
Expected research plan funding payments							13,500,000
Remaining deferred revenue					$ 6,400,000		6,400,000
Amount of expected research plan funding payments of per active target per year							1,000,000
Restated Roche Agreement Accounting | Target Two
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment received		$ 2,000,000
Transaction price allocated to performance obligations					61,900,000		$ 61,900,000
Restated Roche Agreement Accounting | Targets 3
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of material rights | MaterialRight							3
Transaction price allocated to performance obligations					4,700,000		$ 4,700,000
Restated Roche Agreement Accounting | Targets 4-6
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated to performance obligations					28,600,000		28,600,000
Restated Roche Agreement Accounting | Targets 1-3
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated to performance obligations					$ 28,600,000		28,600,000
Restated Roche Agreement Accounting | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount of expected research plan funding payments of per target							$ 3,000,000
Biogen License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of additional targets | Target							2
Number of targets | Target					5		5
Number of performance obligation | Performanceobligation					1		1
Agreement date			2018-12
Research agreement, period			54 months				54 months
Additional payment on extension of contract			$ 62,500,000
Nonrefundable upfront payment							$ 45,000,000
Written notice period for termination of agreement							90 days
Revenue recognized					$ 600,000	$ 200,000	$ 2,000,000	$ 200,000
Biogen License Agreement | Accounts Receivable and Deferred Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment									$ 4,000,000
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
Biogen License Agreement | Maximum | Research And Development Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received							$ 35,000,000
Biogen License Agreement | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Written notice period for termination of agreement							90 days
Calico License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment							$ 5,000,000
Number of targets | Target					5		5
Number of performance obligation | Performanceobligation					1		1
Research term								5 years
Annual Payments							$ 5,000,000
Contractual term							5 years
Calico License Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of target proteins | TargetProtein					5		5
Calico License Agreement | Maximum | One-Time Sales-Based Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received							$ 65,000,000
Calico License Agreement | Maximum | Potential Research, Development and Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received							$ 132,000,000