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Significant Accounting Policies (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Share-based Compensation      
Expected term 6 years 3 months 6 years 3 months  
Level 1      
Fair Value Measurements      
Carrying value of cash held in money market fund $ 147.8   $ 156.2
Level 2      
Fair Value Measurements      
Assets measured at fair value levels 2 or 3 0.0   0.0
Liabilities measured at fair value levels 2 or 3 0.0   0.0
Level 3      
Fair Value Measurements      
Assets measured at fair value levels 2 or 3 0.0   0.0
Liabilities measured at fair value levels 2 or 3 $ 0.0   $ 0.0
Maximum      
Share-based Compensation      
Expiration period 10 years