Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation - Summary of Activity of Restricted Stock Units (Detail)

v3.19.1
Stock-Based Compensation - Summary of Activity of Restricted Stock Units (Detail) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted-average grant date fair value, Granted $ 16.76 $ 8.00
Restricted Stock Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted stock units outstanding, Unvested beginning balance 1,373,933  
Number of restricted stock units outstanding, Granted 315,825  
Number of restricted stock units outstanding, Vested (261,507)  
Number of restricted stock units outstanding, Cancelled (376,837)  
Number of restricted stock units outstanding, Unvested ending balance 1,051,414 1,373,933
Weighted-average grant date fair value, Unvested beginning balance $ 8.00  
Weighted-average grant date fair value, Granted 16.76  
Weighted-average grant date fair value, Vested 9.89  
Weighted-average grant date fair value, Cancelled 10.72  
Weighted-average grant date fair value, Unvested ending balance $ 10.15 $ 8.00