Significant Agreements - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Jun. 30, 2020	Sep. 30, 2018	Dec. 31, 2018
Series B Redeemable Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Redeemable convertible preferred stock, shares issued			7,081,452
Issuance of redeemable convertible preferred stock, value			$ 93,844,000
License Agreement | Novartis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payments for license agreement		$ 2,500,000
License Agreement | Novartis | Series B Redeemable Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Redeemable convertible preferred stock, shares issued		263,615
Issuance of redeemable convertible preferred stock, value		$ 3,800,000
Maximum | License Agreement | Novartis
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent development and sales milestone payments		$ 29,000,000
GSK Collaboration Agreement | GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 100,000,000
Number of business days within upfront payment to be received from effective date	10 days
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
Commercial milestone payment eligible to receive	475,000,000
MAT2A Program | GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise payment agreed to be received	$ 50,000,000
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
Commercial milestone payment eligible to receive	$ 475,000,000
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
Development milestone payment eligible to receive	$ 485,000,000
WRN Program | GSK
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs sharing percentage	80.00%