Quarterly report pursuant to Section 13 or 15(d)

Stock Plans - Additional Information (Detail)

v3.10.0.1
Stock Plans - Additional Information (Detail) - USD ($)
 1 Months Ended 9 Months Ended
Jun. 29, 2018
Jan. 31, 2018
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Class of Stock [Line Items]          
Accrued employee contributions     $ 2,610,000   $ 3,117,000
2018 Performance- Based Stock Incentive Plan [Member]          
Class of Stock [Line Items]          
Number of shares authorized for issuance     4,200,000    
Total grant date fair value of stock options vested $ 30,375,000        
2018 Performance- Based Stock Incentive Plan [Member] | Chad Steelberg and Ryan Steelberg [Member]          
Class of Stock [Line Items]          
Options exercise Period     30 days    
Options exercise price     $ 21.25    
Term of options     10 years    
2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]          
Class of Stock [Line Items]          
Options exercise price     $ 14.22    
Unrecognized compensation expense related to stock options     $ 20,831,000    
Employee Stock Purchase Plan [Member]          
Class of Stock [Line Items]          
Common stock granted   44,842      
Accrued employee contributions     $ 200,000    
Performance-based Stock Options [Member] | 2018 Performance- Based Stock Incentive Plan [Member]          
Class of Stock [Line Items]          
Options exercise price     $ 21.25    
Total grant date fair value of stock options vested     $ 0    
Cost of share-based compensation awards, recognition period     4 years 1 month 6 days    
Weighted Average Grant Date Fair Value, Granted     $ 9.59    
Unrecognized compensation expense related to stock options     $ 28,434,000    
Performance-based Stock Options [Member] | 2018 Performance- Based Stock Incentive Plan [Member] | Chad Steelberg [Member]          
Class of Stock [Line Items]          
Common stock granted     1,809,900    
Performance-based Stock Options [Member] | 2018 Performance- Based Stock Incentive Plan [Member] | Ryan Steelberg [Member]          
Class of Stock [Line Items]          
Common stock granted     1,357,425    
Restricted Stock [Member] | 2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]          
Class of Stock [Line Items]          
Unrecognized cost of share-based compensation awards     $ 533,000    
Cost of share-based compensation awards, recognition period     1 year 8 months 12 days    
Restricted Stock Units [Member] | 2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]          
Class of Stock [Line Items]          
Unrecognized cost of share-based compensation awards     $ 435,000    
Cost of share-based compensation awards, recognition period     9 months 18 days    
Stock Options [Member]          
Class of Stock [Line Items]          
Total grant date fair value of stock options vested     $ 6,711,000 $ 11,451,000  
Weighted Average Grant Date Fair Value, Granted     $ 7.90 $ 8.72  
Aggregate intrinsic value of the options exercised     $ 1,964,000 $ 32,000  
Stock Options [Member] | 2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]          
Class of Stock [Line Items]          
Cost of share-based compensation awards, recognition period     2 years 6 months