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Condensed Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Income Statement [Abstract]        
Unrealized loss on investments, tax $ 0 $ 0 $ 0 $ 0