Annual report pursuant to Section 13 and 15(d)

Stock Plans - Additional Information (Detail)

v3.20.1
Stock Plans - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Apr. 30, 2017
Dec. 31, 2019
Dec. 31, 2018
Class of Stock [Line Items]      
Employee payroll deductions accrued   $ 2,486,000 $ 6,570,000
Performance-based Stock Options [Member]      
Class of Stock [Line Items]      
Cost of share-based compensation awards, recognition period   3 years  
Weighted Average Grant Date Fair Value, Granted   $ 2.55 $ 9.59
Total grant date fair value of stock options vested   $ 0 $ 0
Unrecognized compensation expense related to stock options   $ 21,493,000  
Timebased Stock Option [Member]      
Class of Stock [Line Items]      
Vesting period   4 years  
Maximum [Member] | Restricted Stock Units [Member]      
Class of Stock [Line Items]      
Vesting period   2 years  
Minimum [Member] | Restricted Stock Units [Member]      
Class of Stock [Line Items]      
Vesting period   1 year  
2017 Stock Incentive Plan [Member]      
Class of Stock [Line Items]      
Common stock reserved for future issuance 2,000,000 754,111  
Annual shares increase for future issuance by percentage under employee stock purchase plans 3.00%    
2017 Stock Incentive Plan [Member] | Performance-based Stock Options [Member]      
Class of Stock [Line Items]      
Vesting period   30 days  
2017 Stock Incentive Plan [Member] | Timebased Stock Option [Member]      
Class of Stock [Line Items]      
Vesting period   3 years  
2017 Stock Incentive Plan [Member] | Restricted Stock Units [Member]      
Class of Stock [Line Items]      
Vesting period   1 year  
2017 Stock Incentive Plan [Member] | Maximum [Member]      
Class of Stock [Line Items]      
Increase in common stock reserved for future issuance 750,000    
2018 Performance-Based Stock Incentive Plan [Member]      
Class of Stock [Line Items]      
Common stock reserved for future issuance   183  
Number of shares authorized for issuance   4,200,000  
Stock options, expiration period   10 years  
2018 Performance-Based Stock Incentive Plan [Member] | Performance-based Stock Options [Member] | Chad Steelberg [Member]      
Class of Stock [Line Items]      
Common stock granted   1,809,900  
2018 Performance-Based Stock Incentive Plan [Member] | Performance-based Stock Options [Member] | Ryan Steelberg [Member]      
Class of Stock [Line Items]      
Common stock granted   1,357,425  
2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]      
Class of Stock [Line Items]      
Stock options, expiration period   10 years  
2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member] | Restricted Stock Units [Member]      
Class of Stock [Line Items]      
Unrecognized cost of share-based compensation awards   $ 372,000  
Cost of share-based compensation awards, recognition period   10 months 24 days  
Restricted stock granted   162,211  
Fair value of restricted stock vested   $ 362,000 $ 901,000
Weighted Average Grant Date Fair Value, Granted   $ 6.97 $ 13.46
2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member] | Stock Options [Member]      
Class of Stock [Line Items]      
Cost of share-based compensation awards, recognition period   1 year 10 months 24 days  
Weighted Average Grant Date Fair Value, Granted   $ 3.47 $ 7.40
Total grant date fair value of stock options vested   $ 10,226,000 $ 8,929,000
Unrecognized compensation expense related to stock options   8,137,000  
Aggregate intrinsic value of the options exercised   $ 189,000 $ 1,984,000
2018 Stock Incentive Plan [Member] | Performance-based Stock Options [Member]      
Class of Stock [Line Items]      
Vesting period   30 days  
Stock Plan [Member] | Restricted Stock [Member]      
Class of Stock [Line Items]      
Unrecognized cost of share-based compensation awards   $ 150,000  
Cost of share-based compensation awards, recognition period   9 months 18 days  
Restricted stock granted   0 0
Fair value of restricted stock vested   $ 299 $ 1,022
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%    
Number of shares authorized for issuance 200,000    
ESPP offering description   Under the ESPP, each offering period is generally 24 months with four, six-month purchase intervals, and new offering periods generally commence every six months, as determined by the Compensation Committee of the Board of Directors.  
Maximum number of shares per employee in each purchase 1,000    
Employee payroll deductions accrued   $ 196,000 $ 448,000
Common stock were purchased under ESPP   80,654 129,514
Weighted average purchase price   $ 12.72 $ 4.65
Employee Stock Purchase Plan [Member] | Maximum [Member]      
Class of Stock [Line Items]      
Increase in common stock reserved for future issuance 250,000    
Employee Stock Purchase Plan [Member] | Minimum [Member]      
Class of Stock [Line Items]      
Percentage of purchase price of common stock fair value 85.00%