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Marketable Equity Investments - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Apr. 30, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Investment [Line Items] |  |  |  |
Eligibility to receive a royalty fee |  | 1.00% |  |
Royalty income, nonoperating |  | $ 0 | $ 0 | $ 0
Carrying value of investment |  | 0 |  |
Gain on sale of investment in marketable equity securities |  | $ 3,466,000 | $ 750,000 |
Remaining investment in common stock |  | 103,475,000 | 103,475,000 |
Aduro |  |  |  |
Investment [Line Items] |  |  |  |
Preferred shares converted to common stock | 396,700 |  |  |
Sale of common stock in marketable equity investment |  | 346,700 | 50,000 |
Gain on sale of investment in marketable equity securities |  | $ 3,500,000 | $ 800,000 |
Remaining investment in common stock |  | 0 |  |

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- Definition Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75025870&loc=d3e40691-111596 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 35 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=75027002&loc=d3e40346-111594 + Details
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