Investments in Marketable Securities - Gross Realized Gains and Losses from Sale of Available for Sale Securities (Detail) - USD ($) $ in Thousands |
12 Months Ended | |
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Dec. 31, 2017 |
Dec. 31, 2016 |
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| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||
| Gross realized gains | $ 2 | $ 43 |
| Gross realized losses | $ 0 | $ (166) |
| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition This item represents the gross profit 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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| X | ||||||||||
- 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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