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Commitments and Contingencies - Additional Information (Detail) - USD ($) | Dec. 31, 2018 | Dec. 31, 2017
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Loss Contingencies [Line Items] |  |
Purchase commitments related to contract manufacturing, clinical development and certain other items | $ 63,300,000 |
Putative Securities Class Action [Member] |  |
Loss Contingencies [Line Items] |  |
Litigation matters, liabilities | 0 |
Indemnification Obligation [Member] |  |
Loss Contingencies [Line Items] |  |
Litigation matters, liabilities | 0 | $ 0
Merger and Acquisition Related Claims [Member] | Maximum [Member] |  |
Loss Contingencies [Line Items] |  |
Obligations under Director and Officer Indemnifications per incident | 2,500,000 |
Securities Related Claims [Member] |  |
Loss Contingencies [Line Items] |  |
Obligations under Director and Officer Indemnifications per incident | 2,500,000 |
Non-Securities Related Claims [Member] |  |
Loss Contingencies [Line Items] |  |
Obligations under Director and Officer Indemnifications per incident | $ 1,250,000 |

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