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Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 1 Months Ended |  |  |
--- | --- | --- | --- | ---
Apr. 30, 2018 | Mar. 31, 2019 | May 31, 2017 | Dec. 07, 2016
ATM Agreement [Member] |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |
Common stock issuable and sellable under offering agreement |  | $ 75.0 | $ 75.0 | $ 75.0
Common Stock [Member] |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |
Total shares issued | 14.2 |  |  |
Public offering price of common stock issued | $ 16.25 |  |  |
Net proceeds from issuance of common stock, after deducting offering expenses | $ 215.8 |  |  |

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