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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
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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

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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition Description of time deposit maturities, including certificates of deposit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 + Details
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- Definition Period of time between issuance and maturity of customer deposits, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher SEC -Name Industry Guide -Number 3 -Section V -Paragraph D-E + Details
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