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Employee Benefit Plan - Additional Information (Detail) - USD ($) | 12 Months Ended | 96 Months Ended
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Retirement Benefits [Abstract] |  |  |
Company matched employee's contribution | 50.00% | 25.00% | 25.00%
Employee's contribution | $ 4,000 | $ 3,000 | $ 2,000

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- References No definition available. + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Definition Maximum amount the employee may contribute to a defined contribution plan. + References No definition available. + Details
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