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Short-Term Investments - Schedule of Marketable Debt Securities (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Unrealized gains  
US Treasury Bond [Member]      
Amortized Cost   2,503
Unrealized gains   [1]
Realized gains  
Fair value   $ 2,503
[1] Less than 1