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Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, $ in Thousands | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | ---
Aug. 31, 2018 USD ($) Program | Jun. 30, 2020 $ / shares | Mar. 31, 2020 USD ($) | Jun. 30, 2019 $ / shares | Jun. 30, 2020 USD ($) $ / shares | Jun. 30, 2019 USD ($) $ / shares | Jun. 16, 2020
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Net income |  |  |  |  |  | $ (10,277) | $ 28,043 |
Net income (loss) per share, basic | $ / shares | [1] |  | $ 1.00 |  | $ (0.60) | $ 0.39 | $ (1.22) |
Net income (loss) per share, diluted | $ / shares | [1] |  | $ 0.94 |  | $ (0.60) | $ 0.36 | $ (1.22) |
Fair Value Measurements Recurring | Level 2 | Measurement Input Discount for Lack of Marketability |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Alternative investment, measurement input |  |  |  |  |  |  |  | 5.4
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 |  |  |  |  |  | $ 3,600 |  |
Net income |  |  |  |  |  | $ 3,600 |  |
Net income (loss) per share, basic | $ / shares |  |  |  |  |  | $ 0.14 |  |
Net income (loss) per share, diluted | $ / shares |  |  |  |  |  | $ 0.13 |  |
[1] | See Notes 2 and 10 for an explanation of the calculations of our basic and diluted net income (loss) per share, basic and diluted and the weighted-average number of shares used in the computation of the per share amounts.

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