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Stock-Based Compensation - Additional Information (Detail)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
Jun. 30, 2020
shares
Jun. 30, 2019
shares
Dec. 31, 2020
USD ($)
Period
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Total intrinsic value of options exercised | $     $ 7.9 $ 1.6 $ 7.1
Stock-based compensation, expected dividend yield     0.00%    
Weighted average grant-date fair value of stock options granted | $ / shares     $ 2.71 $ 2.73 $ 2.41
Stock Options          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense expected to be recognized | $     $ 7.0    
Stock-based compensation, weighted average recognition period     2 years 3 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 | $     $ 18.2    
Stock-based compensation, weighted average recognition period     1 year 9 months 18 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    
Increase in shares of common stock authorized for issuance 1,500,000        
Aggregate number of shares of common stock reserved for future issuance     1,800,000    
Stock-based compensation, expected dividend yield     0.00% 0.00% 0.00%
Weighted average grant-date fair value of awards granted | $ / shares     $ 1.71 $ 1.84 $ 2.29
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%    
Increase in shares of common stock authorized for issuance 5,000,000.0 11,800,000      
Aggregate number of shares of common stock reserved for future issuance     30,500,000    
Stock-based compensation, award term     10 years    
Performance-based stock options, outstanding     20,000    
Outstanding options and other stock based awards     16,306,000 16,830,000  
Number of shares available for future issuance     8,400,000    
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     5,739,000 4,098,000  
Total fair value | $     $ 6.8 $ 5.6 $ 2.8
Weighted average grant-date fair value of awards granted | $ / shares [1]     $ 5.17    
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.