License and Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Dec. 21, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, $0.0001 par value, 198,000,000 shares authorized; 78,432,246 and 75,184,863 issued and outstanding at June 30, 2020 and December 31, 2019, respectively		$ 8		$ 8		$ 8
Revenue		111,344	$ 94,668	$ 211,792	$ 181,679
License and Collaboration Agreements [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment for option exercise		129,000
Stock Options Exercised or Expired				0
Development Milestone and Upfront Fee Recognized as Research and Development Expense		12,800	$ 14,400	$ 21,300	$ 15,500
License and Collaboration Agreements [Member] | Research And Development Expense [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment made		12,000
License and Collaboration Agreements [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent research milestone payments		14,000
Development, regulatory, commercial milestone and up-front royalty payments		3,200,000		$ 3,200,000
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	$ 485,000
Single combined performance obligation	348,700
Common stock, $0.0001 par value, 198,000,000 shares authorized; 78,432,246 and 75,184,863 issued and outstanding at June 30, 2020 and December 31, 2019, respectively	312,100
Direct Transaction Fees	4,300
Stock Options Exercised or Expired				0
Revenue		26,000		$ 39,200
Deferred Revenue		797,700		797,700
Deferred Revenue, Current		89,200		89,200
Deferred Revenue Separate Material Options Right		485,000		485,000
Research and development expense		$ 8,900		25,400
License and Collaboration Agreements [Member] | Roche | Accounts Receivable [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense				$ 8,900
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