Quarterly report pursuant to Section 13 or 15(d)

Quarterly report pursuant to Section 13 or 15(d)

Equity - Narrative (Detail)

v3.10.0.1
Equity - Narrative (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
May 25, 2017
May 24, 2017
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock option outstanding (in shares)     7,455,054   7,455,054   6,342,526
Stock options, granted (in shares)         2,168,602    
Unrecognized stock-based compensation cost     $ 4.5   $ 4.5    
Unrecognized share-based compensation expense, weighted-average recognition period (in years)         9 months    
Employee Stock Purchase Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Change in discount rate 15.00% 5.00%          
Shares purchased by employees under ESPP     29,266 26,569 66,188 50,932  
Stock compensation expense (gain)     $ 0.1 $ 0.0 $ 0.1 $ 0.0  
Non Employee              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock options, granted (in shares)         840,001    
Stock option vested (in shares)         416,663    
Stock option unvested (in shares)     423,338   423,338