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Stock-Based Compensation - Summary of Compensation Expense by Type of Award (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total stock-based compensation $ 753 $ 688 $ 2,292 $ 2,604
Stock Options [Member]        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total stock-based compensation 514 503 1,556 2,101
ESPP [Member]        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total stock-based compensation $ 239 $ 185 $ 736 $ 503