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Fair Value Measurements and Short-Term Investments - Schedule of Short-term Investments (Details) - U.S treasury securities
$ in Thousands
Mar. 31, 2019
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Amortized Cost $ 79,321
Gross Unrealized  
Gains 0
Losses (8)
Estimated Fair Value $ 79,313