Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Schedule of Stock-based Compensation Related to All Employee And Non-employee Stock Awards (Detail)

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Stockholders' Equity - Schedule of Stock-based Compensation Related to All Employee And Non-employee Stock Awards (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]    
Total stock-based compensation expense $ 7,014 $ 5,347
Research and development    
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]    
Total stock-based compensation expense 2,932 2,141
General and administrative    
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]    
Total stock-based compensation expense $ 4,082 $ 3,206