Investments in Marketable Securities - Additional Information (Detail) - USD ($) |
12 Months Ended | |
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Dec. 31, 2017 |
Dec. 31, 2016 |
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Gross realized loss | $ 0 | $ 166,000 |
| Investments other-than-temporarily impaired | $ 0 | |
| Sale of Available-For-Sale, Marketable Security that No Longer Met Investment Policy [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Gross realized loss | $ 152,000 | |
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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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- Details
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