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Shareholders' Deficit - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 23, 2020
May 26, 2020
Jun. 30, 2020
May 31, 2020
Jun. 30, 2020
Mar. 31, 2020
Jun. 30, 2020
Dec. 31, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Class Of Stock [Line Items]                      
Proceeds from issuance of warrant             $ 15,000        
Net proceeds from issuance of common shares in initial public offering             $ 233,760        
Common stock shares issued     36,753,454   36,753,454   36,753,454 1,528,374      
Number of options exercised             266,687        
Options, weighted-average exercise price             $ 1.83        
Aggregate proceeds from exercise of options             $ 488        
Decrease in additional paid-in capital as exercised options credited to common shares             289        
Unrecognized share-based compensation expense related to unvested stock options     $ 11,837   $ 11,837   $ 11,837        
Unrecognized share-based compensation expense related to unvested stock options, recognition period             3 years        
2020 Employee Share Purchase Plan                      
Class Of Stock [Line Items]                      
Annual increase in number of shares available for issuance as percentage of outstanding shares common stock on final day of preceding calendar year     1.00%                
Common stock shares issued     0   0   0        
Annual increase in number of shares available for issuance maximum number of common stock issued     3,300,000                
Purchase price of shares as percentage of fair market value of common stock on date of purchase     85.00%                
Option Plan                      
Class Of Stock [Line Items]                      
Shares of common stock reserved for future issuance     298,605   298,605   298,605        
2020 Equity Incentive Plan                      
Class Of Stock [Line Items]                      
Annual increase in number of shares available for issuance as percentage of outstanding shares common stock on final day of preceding calendar year     5.00%                
Exercise price per share as minimum percentage of fair value of common share 100.00%                    
Expiration period 10 years                    
Monthly vesting rate 1/36th                    
2020 Equity Incentive Plan | Vesting on First Anniversary Date of Grant                      
Class Of Stock [Line Items]                      
Vesting percentage 25.00%                    
2020 Equity Incentive Plan | Vesting on Monthly Basis at Rate of 1/36th                      
Class Of Stock [Line Items]                      
Vesting percentage 75.00%                    
Maximum | 2020 Employee Share Purchase Plan                      
Class Of Stock [Line Items]                      
Shares of common stock reserved for future issuance     327,000   327,000   327,000        
Maximum | 2020 Equity Incentive Plan                      
Class Of Stock [Line Items]                      
Shares of common stock reserved for future issuance     3,807,448   3,807,448   3,807,448        
Shares of common stock initially reserved for future issuance     3,600,000   3,600,000   3,600,000        
Affiliate of Bristol Myers Squibb                      
Class Of Stock [Line Items]                      
Proceeds from issuance of warrant   $ 15,000   $ 15,000              
Affiliate of Bristol Myers Squibb | Initial Public Offering                      
Class Of Stock [Line Items]                      
Warrant exercise price per share $ 20.00                    
Series A Convertible Preferred Shares                      
Class Of Stock [Line Items]                      
Temporary equity shares authorized               Unlimited      
Temporary equity shares issued     0   0   0 11,090,135      
Temporary equity shares outstanding     0   0 11,090,135 0 11,090,135 11,090,135 11,090,135 6,813,340
Series B Convertible Preferred Shares                      
Class Of Stock [Line Items]                      
Temporary equity shares authorized               Unlimited      
Temporary equity shares issued     0   0   0 10,468,258      
Temporary equity shares outstanding     0   0 10,468,258 0 10,468,258      
Common Shares                      
Class Of Stock [Line Items]                      
Preferred shares converted into common shares 21,558,393           21,558,393        
Shares issued upon exercise of warrants outstanding 750,000                    
Shares issued, price per share $ 20.00                    
Gross proceeds from IPO $ 253,000                    
Net proceeds from issuance of common shares in initial public offering $ 232,043                    
Number of options exercised         85,369 181,318          
Common Shares | Option Plan                      
Class Of Stock [Line Items]                      
Number of shares authorized to be issued     4,074,135   4,074,135   4,074,135        
Common Shares | Initial Public Offering                      
Class Of Stock [Line Items]                      
Issuance of common shares upon initial public offering, Shares 12,650,000       12,650,000            
Common Shares | Exercise of Underwriters Option                      
Class Of Stock [Line Items]                      
Issuance of common shares upon initial public offering, Shares 1,650,000                    
Common Shares | Exercise of Underwriters Option | Maximum                      
Class Of Stock [Line Items]                      
Issuance of common shares upon initial public offering, Shares 1,650,000                    
Common Shares | Affiliate of Bristol Myers Squibb                      
Class Of Stock [Line Items]                      
Shares issued upon exercise of warrants outstanding 750,000