Cash Equivalents and Marketable Securities - Additional Information (Details) - USD ($) |
3 Months Ended | 9 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
Dec. 31, 2018 |
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| Cash And Cash Equivalents [Line Items] | |||||
| Long-term marketable securities | $ 25,223,000 | $ 25,223,000 | |||
| Recognition of other-than-temporary impairment | 0 | $ 0 | 0 | $ 0 | |
| Investments in an unrealized loss position | $ 20,100,000 | $ 20,100,000 | $ 52,600,000 | ||
| Marketable Securities | |||||
| Cash And Cash Equivalents [Line Items] | |||||
| Recognition of other-than-temporary impairment | $ 0 | ||||
| Maximum [Member] | |||||
| Cash And Cash Equivalents [Line Items] | |||||
| Marketable securities maturity period | 1 year | 1 year | |||
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- Definition Marketable securities maturity period. No definition available.
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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- Definition Amount of investment in marketable security, classified as noncurrent. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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