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Agreements - Additional Information (Detail) - License Agreement with BioMarin [Member]
$ in Millions
 9 Months Ended
Sep. 30, 2020
USD ($)
License Agreement [Line Items]  
Date on which strategic collaboration is entered into Oct. 26, 2012
Royalty agreement period 7 years
Net sales royalty threshold $ 100
Minimum [Member]  
License Agreement [Line Items]  
Percentage of royalty on net sales 7.00%
Maximum [Member]  
License Agreement [Line Items]  
Percentage of royalty on net sales 10.00%