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Available-for-sale Securities and Fair Value on Financial Instruments - Additional Information (Detail) - USD ($) | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items] |  |  |
Available-for-sale securities in unrealized net loss position | $ 0 | $ 283,000 |
Other-than-temporary impairment losses | $ 0 | $ 0 | $ 0
Remaining investment in common stock | 144,291,000 | 136,853,000 |
Gross realized losses from the sale or maturity of available-for-sale investments | $ 0 | $ 0 | 0
Aduro Biotech Inc |  |  |
Schedule Of Available For Sale Securities [Line Items] |  |  |
Gross realized gains from the sale of available-for-sale investments | $ 0 | $ 0 | $ 3,500,000
Sale of common stock available-for-sale investments | 0 | 0 | 346,700
Remaining investment in common stock | 0 | 0 |

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