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Financial Instruments (Narrative) (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Financial Instruments [Line Items] |  |  |  |
Realized loss or gains | $ 0 | $ 0 | $ 0 | $ 0
US Treasury and Government Short-term Debt Securities [Member] |  |  |  |
Financial Instruments [Line Items] |  |  |  |
Available for Sale Securities Maturity Period |  |  | 3 years |

X
- Definition Number of maturity year relating to investment securities. + References No definition available. + Details
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X
- References No definition available. + Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of realized gain (loss) on investment in debt and equity securities. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
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X
- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |