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Short-Term Investments - Additional Information (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Short Term Investments [Abstract]        
Debt securities, impairment losses $ 0 $ 0 $ 0 $ 0
Debt securities, realized gain and (losses) $ 0 $ 0 $ 8,000 $ 0