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Shareholders' Deficit - Narrative (Details) - USD ($)
3 Months Ended 9 Months Ended
Jun. 04, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Apr. 30, 2018
Subsidiary, Sale of Stock [Line Items]            
Cash, cash equivalents and marketable securities   $ 745,800,000   $ 745,800,000    
Public Offering            
Subsidiary, Sale of Stock [Line Items]            
Number of shares issued (in shares) 17,424,243          
Price of shares (in USD per share) $ 8.25          
Net proceeds from sale of shares $ 134,500,000          
Cowen and Company, LLC | Private Placement            
Subsidiary, Sale of Stock [Line Items]            
Aggregate offering price           $ 100,000,000.0
Number of shares issued (in shares)   0 0 0 106,494  
Price of shares (in USD per share)     $ 24.65   $ 24.65  
Net proceeds from sale of shares         $ 2,500,000  
Remaining capacity in offering program   $ 10,400,000   $ 10,400,000