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Financial Instruments and Risk - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017
Schedule Of Cost Method Investments [Line Items] |
Average days to maturity of Company's portfolio of cash equivalents and marketable securities | 0 days
Maximum [Member] |
Schedule Of Cost Method Investments [Line Items] |
Maturity period of securities | 1 year

X
- Definition Average period to maturity for portfolio of cash and marketable securities. + References No definition available. + Details
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X
- Definition Maturity period of securities. + References No definition available. + Details
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X
- 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. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
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Period Type: |