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Non-Marketable Equity Investments - Additional Information (Detail) - USD ($) $ in Thousands | 9 Months Ended |  |
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2019 | Dec. 31, 2018
Investments Debt And Equity Securities [Abstract] |  |  |
Reduction to carrying value of non-marketable equity investment due to downward change in fair value | $ 1,271 |  |
Aggregate carrying amount of non-marketable equity investments |  | $ 5,400 | $ 2,100

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- Definition Amount of investment in equity security without readily determinable fair value. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117539-209714 + Details
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