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The Company - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands |  |  | 12 Months Ended
--- | --- | --- | ---
Aug. 24, 2017 | Apr. 11, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Business Description [Line Items] |  |  |  |  |
Net proceeds from offering |  |  | $ 34,910 | $ 9,881 | $ 14,992
Follow On Offering |  |  |  |  |
Business Description [Line Items] |  |  |  |  |
Common stock shares sold | 9,200,000 | 5,228,750 |  |  |
Public offering price | $ 40.75 | $ 22.95 |  |  |
Net proceeds from offering | $ 356,200 | $ 115,100 |  |  |
Underwriting discounts and commissions | 18,700 | 4,900 |  |  |
Offering expenses | $ 400 | $ 600 |  |  |

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