Annual report pursuant to Section 13 and 15(d)

Stock Plans - Additional Information (Detail)

v3.8.0.1
Stock Plans - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
May 31, 2017
Apr. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Class of Stock [Line Items]        
Stock-based compensation expense     $ 16,089,000 $ 1,730,000
Expected forfeitures rate     10.00% 10.00%
Accrued employee contributions     $ 3,117,000 $ 500,000
2017 Stock Incentive Plan [Member]        
Class of Stock [Line Items]        
Common stock reserved for future issuance   2,000,000 1,372,767  
Annual shares increase for future issuance by percentage under employee stock purchase plans   3.00%    
Vesting period     1 year  
2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]        
Class of Stock [Line Items]        
Vesting period     4 years  
Options Granted     4,383,208  
Options exercise price     $ 15.27  
Unrecognized compensation expense related to stock options     $ 23,408,000  
Employee Stock Purchase Plan [Member]        
Class of Stock [Line Items]        
Common stock reserved for future issuance   1,000,000    
Annual shares increase for future issuance by percentage under employee stock purchase plans   1.00%    
Maximum number of shares per employee in each purchase   1,000    
Accrued employee contributions     $ 253,000  
Common stock granted     0  
Time-based Stock Option [Member] | Chad Steelberg and Ryan Steelberg [Member]        
Class of Stock [Line Items]        
Vesting period 3 years      
Options Granted 2,089,638      
Options exercise price $ 15      
Performance- based Stock Option [Member]        
Class of Stock [Line Items]        
Stock-based compensation expense     $ 9,282,000  
Performance- based Stock Option [Member] | Chad Steelberg and Ryan Steelberg [Member]        
Class of Stock [Line Items]        
Vesting period 5 years      
Options Granted 1,044,818      
Options exercise price $ 15      
Vesting rights description The performance-based stock options were to vest upon the earlier of the first date on which the market capitalization of the Company's common stock equaled or exceeded $400,000 over five consecutive business days, or five years after the IPO      
Vesting rights, market capitalization $ 400,000      
Vesting rights, consecutive trading days 5 days      
Restricted Stock [Member]        
Class of Stock [Line Items]        
Stock-based compensation expense     $ 891,000 $ 151,000
Weighted Average Grant Date Fair Value, Granted     $ 15.47 $ 4.71
Fair value of restricted stock vested     $ 2,185 $ 243
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     $ 1,030,000  
Cost of share-based compensation awards, recognition period     2 years 2 months 12 days  
Weighted Average Grant Date Fair Value, Granted     $ 15.47  
Restricted Stock Units [Member]        
Class of Stock [Line Items]        
Stock-based compensation expense     $ 327,000  
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     $ 197,000  
Cost of share-based compensation awards, recognition period     4 months 24 days  
Weighted Average Grant Date Fair Value, Granted     $ 14.76  
Stock Options [Member]        
Class of Stock [Line Items]        
Stock-based compensation expense     $ 14,391,000 $ 137,000
Weighted Average Grant Date Fair Value, Granted     $ 8.95 $ 2.14
Aggregate intrinsic value of the options exercised     $ 1,875 $ 258
Total grant date fair value of stock options vested     $ 13,094 $ 95
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 9 months 18 days  
Maximum [Member] | 2017 Stock Incentive Plan [Member]        
Class of Stock [Line Items]        
Increase in common stock reserved for future issuance   750,000    
Maximum [Member] | Employee Stock Purchase Plan [Member]        
Class of Stock [Line Items]        
Increase in common stock reserved for future issuance   250,000    
Minimum [Member] | Employee Stock Purchase Plan [Member]        
Class of Stock [Line Items]        
Percentage of purchase price of common stock fair value   85.00%    
Common stock fair market value   $ 25