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Stock-Based Compensation - Summary of Compensation Expense by Type of Award (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total stock-based compensation $ 766 $ 1,180 $ 1,539 $ 1,916
Stock Options [Member]        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total stock-based compensation 509 1,005 1,042 1,598
ESPP [Member]        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Total stock-based compensation $ 257 $ 175 $ 497 $ 318