XML 84 R68.htm IDEA: XBRL DOCUMENT v3.19.1
Stock-Based Compensation - Summary of Stock-Based Compensation Expense Classification (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Stock-based compensation expense $ 262 $ 128
Research and Development Expenses [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Stock-based compensation expense 84 38
General and Administrative Expenses [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Stock-based compensation expense $ 178 $ 90