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Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments - Additional Information (Details) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Fair Value Disclosures [Abstract]    
Maturity period of certificates of deposit 1 year 1 year
Maturity of certificates of deposit, description Certificates of deposit at September 30, 2019 and December 31, 2018 had maturity dates of one year or less.  
Liabilities, fair value $ 0 $ 0