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Cash and Marketable Securities - Additional Information (Detail) - USD ($) | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract] |  |  |
Realized losses of available-for-sale securities | $ 0 | $ 0 |
Other-than-temporarily impaired investments | $ 0 |  | $ 0

X
- Definition Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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- Definition Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=109979856&loc=SL6284422-111562 + Details
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