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Summary of Significant Accounting Policies and Basis of Presentation - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2020
USD ($)
Segment
Dec. 31, 2019
USD ($)
Dec. 12, 2019
Jan. 01, 2019
USD ($)
Dec. 31, 2018
USD ($)
Mar. 31, 2016
Feb. 12, 2016
Summary Of Significant Accounting Policies [Line Items]              
Number of operating segments | Segment 1            
Cash and cash equivalents $ 1,168,620,000 $ 943,771,000     $ 456,649,000    
Restricted Cash 16,848,000 5,041,000     3,163,000    
Marketable securities 521,713,000 0.0          
Contract assets 300,000 25,700,000          
Contract liabilities 12,200,000 12,700,000          
Deferred revenue 1,900,000 0          
Net lease assets 50,865,000 41,502,000          
Net lease liabilities 61,429,000 52,539,000          
Significant uncertain tax positions 0 0     $ 0    
Vertex and Casebia [Member] | Collaborative Arrangement [Member]              
Summary Of Significant Accounting Policies [Line Items]              
Other receivables $ 10,700,000 $ 4,100,000          
ASC 326 [Member]              
Summary Of Significant Accounting Policies [Line Items]              
Change in accounting principle, accounting standards update, adopted true            
Change in accounting principle, accounting standards update, adoption date Jan. 01, 2020            
Change in accounting principle, accounting standards update, immaterial effect true            
ASC 606 [Member]              
Summary Of Significant Accounting Policies [Line Items]              
Change in accounting principle, accounting standards update, adopted true            
Change in accounting principle, accounting standards update, adoption date Jan. 01, 2018            
Change in accounting principle, accounting standards update, immaterial effect true            
ASC 842 [Member]              
Summary Of Significant Accounting Policies [Line Items]              
Net lease assets       $ 26,087,000      
Net lease liabilities       $ 37,600,000      
Casebia Therapeutics Limited Liability Partnership [Member]              
Summary Of Significant Accounting Policies [Line Items]              
Equity method investment, ownership percentage     50.00%     50.00% 50.00%