License and Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended
	Dec. 21, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, $0.0001 par value, 99,000,000 shares authorized; 77,957,790 and 75,184,863 issued and outstanding at March 31, 2020, and December 31, 2019, respectively		$ 8		$ 8
Revenue		100,448	$ 87,011
License and Collaboration Agreements [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development Milestone and Upfront Fee Recognized as Research and Development Expense		8,500	$ 1,100
License and Collaboration Agreements [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory, commercial milestone and up-front royalty payments		$ 3,200
License and Collaboration Agreements [Member] | Roche
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds From License And Collaborative Agreement	$ 1,200,000
Stock Issued During Period Value Collaboration and License Agreement	$ 316,300
Stock Issued During Period Shares Collaboration and License Agreement	2,522,227
Payment For Option Exercise	$ 491,000
Single Combined Performance Obligation	342,700
Common stock, $0.0001 par value, 99,000,000 shares authorized; 77,957,790 and 75,184,863 issued and outstanding at March 31, 2020, and December 31, 2019, respectively	312,100
Direct Transaction Fees	4,300
Stock Options Exercised or Expired		0
Revenue		$ 13,200
Deferred Revenue		820,400
Deferred Revenue, Current		87,800
Deferred Revenue Separate Material Options Right		491,000
Research and development expense		$ 16,400
License and Collaboration Agreements [Member] | Roche | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory And Sales Milestones Payment Received	1,700,000
Payment For Option Exercise	125,000
License and Collaboration Agreements [Member] | Roche | Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment For Option Exercise	$ 20,000