Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
Stock-Based Compensation - Summary of Activity of Restricted Stock Units (Detail) - Restricted Stock Units [Member] - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of restricted stock units outstanding, Unvested beginning balance 0    
Number of restricted stock units outstanding, Granted 1,452,333 0 0
Number of restricted stock units outstanding, Vested (39,200)    
Number of restricted stock units outstanding, Cancelled (39,200)    
Number of restricted stock units outstanding, Unvested ending balance 1,373,933 0  
Weighted-average grant date fair value, Unvested beginning balance $ 0    
Weighted-average grant date fair value, Granted 8.00    
Weighted-average grant date fair value, Vested 0    
Weighted-average grant date fair value, Cancelled 0    
Weighted-average grant date fair value, Unvested ending balance $ 8.00 $ 0