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Related Party Transactions - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
May 31, 2019
May 31, 2017
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Novartis International Pharmaceutical Ltd.            
Related Party Transaction [Line Items]            
Payment for development milestone $ 2,500,000 $ 300,000        
Payments to related parties     $ 0 $ 0 $ 0 $ 0
Silverstein Foundation | Funding Agreement            
Related Party Transaction [Line Items]            
Fund received from related parties       $ 0 $ 0 $ 500,000