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Cash, Cash Equivalents and Short-Term Investments - Additional Information (Details) - USD ($) $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
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Cash, Cash Equivalents, and Short-term Investments [Abstract] |  |
Estimated fair value of short-term investments | $ 104,613 | $ 105,266

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- Definition Fair value of investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563 + Details
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