Financial Instruments - Schedule of Marketable Securities That Have Been in Continuous Unrealized Loss Position for Less than 12 months and for 12 months or Greater (Detail) - USD ($) $ in Thousands |
Sep. 30, 2018 |
Dec. 31, 2017 |
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| Cash And Cash Equivalents [Abstract] | ||
| Fair Value of Marketable Securities, Continuous Unrealized Losses, Less than 12 Months | $ 1,987 | $ 39,576 |
| Fair Value of Marketable Securities, Continuous Unrealized Losses, 12 Months or Greater | 15,571 | |
| Fair Value of Marketable Securities, Continuous Unrealized Losses, Total | 17,558 | 39,576 |
| Unrealized Losses, Continuous Unrealized Losses, Less Than 12 Months | (10) | (134) |
| Unrealized Losses, Continuous Unrealized Losses, 12 Months or Greater | (71) | |
| Unrealized Losses, Continuous Unrealized Losses, Total | $ (81) | $ (134) |
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- References No definition available.
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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