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Summary of Significant Accounting Policies - Concentration of Credit Risk (Details)
12 Months Ended
Dec. 31, 2019
USD ($)
fund
Dec. 31, 2018
USD ($)
bank
Cash and Cash Equivalents [Line Items]    
Number of "Triple A" rated money market funds with cash, cash equivalent and restricted cash held on deposit | fund 7  
Money market funds $ 13,653,000 $ 0
Number of global banks with cash, cash equivalent and restricted cash held on deposit | bank   7
Maximum investment limit in any one financial institution 75,000,000  
Cash and cash equivalents $ 193,555,000 $ 165,485,000
Investment in single mutual fund | Credit Concentration Risk    
Cash and Cash Equivalents [Line Items]    
Concentration risk percentage 1.00%