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Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, $ in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Aug. 31, 2018 USD ($) Program | Sep. 30, 2020 USD ($) $ / shares shares | Mar. 31, 2020 USD ($) | Sep. 30, 2019 $ / shares | Sep. 30, 2020 USD ($) $ / shares shares | Sep. 30, 2019 USD ($) $ / shares
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Net income |  |  |  |  | $ (27,416) | $ 40,955
Net income (loss) per share, basic | $ / shares |  | $ 0.46 |  | $ (0.56) | $ 0.91 | $ (1.79)
Net income (loss) per share, diluted | $ / shares |  | $ 0.45 |  | $ (0.56) | $ 0.90 | $ (1.79)
Estimated fair value of equity securities |  | $ 78,872 |  |  | $ 78,872 |
Unrealized gain (loss) on equity securities |  | $ 29,778 |  |  | $ 78,638 |
Fair Value Measurements Recurring | Level 2 | Measurement Input Discount for Lack of Marketability |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Alternative investment, measurement input |  | 0.0225 |  |  | 0.0225 |
Vaxcyte, Inc. | Vaxcyte Common Stock |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Estimated fair value of equity securities |  | $ 78,800 |  |  | $ 78,800 |
Unrealized gain (loss) on equity securities |  | $ 29,700 |  |  | 78,600 |
Vaxcyte, Inc. | Vaxcyte Common Stock | Revaluation of Estimated Fair Value of Vaxcyte Common Stock |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Unrealized gain (loss) on equity securities |  |  |  |  | 78,800 |
Vaxcyte, Inc. | Vaxcyte Common Stock | Revaluation of Prior Preferred Stock Warrant Converted to Common Stock |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Unrealized gain (loss) on equity securities |  |  |  |  | $ (200) |
Vaxcyte, Inc. | Equity Securities | Vaxcyte Common Stock |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Lock-up agreement expires month and year |  |  |  |  | 2020-12 |
Number of shares held | shares |  | 1,634,005 |  |  | 1,634,005 |
ASU 2019-12 |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Change in accounting principle, accounting standards update, early adoption [true false] |  | true |  |  | true |
Change in accounting principle, accounting standards update, adoption date |  | Jan. 01, 2020 |  |  | Jan. 01, 2020 |
Change in accounting principle, accounting standards update, immaterial effect [true false] |  | true |  |  | true |
ASU 2018-13 |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Change in accounting principle, accounting standards update, adoption date |  | Jan. 01, 2020 |  |  | Jan. 01, 2020 |
Change in accounting principle, accounting standards update, immaterial effect [true false] |  | true |  |  | true |
Change in accounting principle, accounting standards update, adopted [true false] |  | true |  |  | true |
2018 Merck Agreement |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Upfront payment received | $ 60,000 |  |  |  |  |
Number of research programs | Program | 2 |  |  |  |  |
Transaction price |  |  | $ 60,000 |  |  |
Revenue recognized performance obligation |  |  | $ 47,100 |  |  |
Number of target programs estimated service period |  |  | 3 years |  |  |
Decrease in revenue due to adjustments |  |  |  |  | $ 800 |
Net income |  |  |  |  | $ 800 |
Net income (loss) per share, basic | $ / shares |  |  |  |  | $ 0.03 |
Net income (loss) per share, diluted | $ / shares |  |  |  |  | $ 0.03 |

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