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Stock-Based Compensation - Additional Information (Detail)
$ / shares in Units, $ in Millions
12 Months Ended
Jun. 05, 2019
shares
Dec. 31, 2019
USD ($)
Period
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total intrinsic value of options exercised | $   $ 1.6 $ 7.1 $ 0.6
Stock-based compensation, expected dividend yield   0.00%    
Weighted average grant-date fair value of stock options granted | $ / shares   $ 2.73 $ 2.41 $ 1.98
Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense expected to be recognized | $   $ 6.0    
Stock-based compensation, weighted average recognition period   1 year 9 months 18 days    
Stock-based compensation, expected dividend yield   0.00% 0.00% 0.00%
Restricted Stock Units (RSUs)        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense expected to be recognized | $   $ 14.1    
Stock-based compensation, weighted average recognition period   1 year 10 months 24 days    
Employee Stock Purchase Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation, option to be granted at percentage of fair value of common stock   85.00%    
Employee Stock Purchase Plan, offering period   12 months    
Number of purchase periods within each offering period | Period   2    
Aggregate number of shares of common stock reserved for future issuance   600,000    
Stock-based compensation, expected dividend yield   0.00% 0.00% 0.00%
Weighted average grant-date fair value of awards granted | $ / shares   $ 1.84 $ 2.29 $ 1.18
2008 Equity Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation, option to be granted at percentage of fair value of common stock   100.00%    
Aggregate number of shares of common stock reserved for future issuance   31,400,000    
Stock-based compensation, award term   10 years    
Performance-based stock options, outstanding   35,000    
Increase in shares of common stock authorized for issuance 11,800,000,000      
Outstanding options and other stock based awards   16,830,000 17,560,000  
Number of shares available for future issuance   10,500,000    
2008 Equity Incentive Plan | Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation, vesting period   4 years    
2008 Equity Incentive Plan | Restricted Stock Units (RSUs)        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of unvested Restricted Stock Units   4,098,000 2,001,000  
Total fair value | $   $ 5.6 $ 2.8 $ 1.0
Weighted average grant-date fair value of awards granted | $ / shares [1]   $ 5.56    
2008 Equity Incentive Plan | Performance-based Stock or Cash Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Employee Stock Purchase Plan, authorized shares for issuance   500,000    
Stock option plan granted on cash award | $   $ 1.0    
2008 Equity Incentive Plan | Minimum | Restricted Stock Units (RSUs)        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation, vesting period   3 years    
2008 Equity Incentive Plan | Maximum | Restricted Stock Units (RSUs)        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation, vesting period   4 years    
[1] Includes shares issuable under performance-based restricted stock unit awards.