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Investments in Marketable Securities - Additional Information (Detail) - USD ($) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Gross realized loss | $ 0 | $ 0 | $ 155,000 | $ 3,000
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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563 + Details
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Balance Type: | debit
Period Type: | duration

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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. + References No definition available. + Details
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- Details
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