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Cash and Cash Equivalents, and Investments - Restricted Cash (Details) - Security Deposit For Office - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]    
Restricted cash $ 1.9 $ 1.3
Restricted cash, current 0.1 0.1
Restricted cash, noncurrent $ 1.8 $ 1.2