Investments in Marketable Securities - Amortized Cost and Fair Value of Investments in Available for Sale Securities (Detail) - USD ($) $ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract] | ||
| Available for sale securities continuous unrealized loss position for less than 12 months, unrealized loss | $ (158) | $ (491) |
| Available for sale securities continuous unrealized loss position for 12 months or longer, unrealized loss | (236) | (37) |
| Available for sale securities continuous unrealized loss position for less than 12 months, fair value | 63,229 | 86,105 |
| Available for sale securities continuous unrealized loss position for 12 months or longer, fair value | $ 44,961 | $ 721 |
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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