Significant Agreements - Additional Information (Details) - USD ($)		1 Months Ended
	Jul. 31, 2020	Jun. 30, 2020	Sep. 30, 2018
Maximum | License Agreement | Novartis International Pharmaceuticals Limited
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent development and sales milestone payments			$ 29,000,000.0
GSK Collaboration Agreement | GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 100,000,000.0
Number of days of notice period for terminating agreement		90 days
MAT2A Program
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs sharing percentage		20.00%
Percentage of profit share		50.00%
MAT2A Program | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development and regulatory milestone payment eligible to receive		$ 465,000,000.0
Commercial milestone payment eligible to receive		475,000,000.0
MAT2A Program | GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise payment agreed to be received		$ 50,000,000.0
Development costs sharing percentage		80.00%
Pol Theta Program | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development and regulatory milestone payment eligible to receive		$ 485,000,000.0
Commercial milestone payment eligible to receive		$ 475,000,000.0
WRN Program
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs sharing percentage		20.00%
Percentage of profit share		50.00%
WRN Program | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Commercial milestone payment eligible to receive		$ 475,000,000.0
Development milestone payment eligible to receive		$ 485,000,000.0
WRN Program | GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs sharing percentage		80.00%