Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans and Stock Based Compensation - Additional Information (Detail)

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Equity Incentive Plans and Stock Based Compensation - Additional Information (Detail) (USD $)
 12 Months Ended 1 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2012
Employee Stock-based Compensation Expense [Member]
Dec. 31, 2011
Employee Stock-based Compensation Expense [Member]
Dec. 31, 2010
Employee Stock-based Compensation Expense [Member]
Mar. 01, 2010
2004 Equity Incentive Plan [Member]
Dec. 31, 2012
2004 Equity Incentive Plan [Member]
Mar. 01, 2010
2004 Equity Incentive Plan [Member]
Board of Directors [Member]
May 19, 2010
2004 Equity Incentive Plan [Member]
Shareholder [Member]
Dec. 31, 2012
2004 Employee Stock Purchase Plan [Member]
Dec. 31, 2011
2004 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of fair market value               100.00%        
Terms of stock options granted               10 years        
Terms of stock options vested               4 years        
Additional shares authorized 1,250,000 1,250,000 2,452,401       202,401   2,250,000 2,250,000    
Percentage of shares issued and outstanding 5.00%                      
Increase in authorized shares 1,250,000                      
Aggregate intrinsic value of options outstanding $ 9,400,000                      
Aggregate intrinsic value of options exercisable 5,800,000                      
Options vested and expected to vest 5,050,008                      
Aggregate intrinsic value of options vested and expected to vest 9,300,000                      
Weighted average remaining contractual life of options vested and expected to vest 8 years                      
Weighted average exercise price of options vested and expected to vest $ 3.16                      
Intrinsic value of stock options exercised 1,700,000 6,000.0 15,000.0                  
Cash received from stock option exercises 600,000 14,000.0 21,000.0                  
Offering period                     24 months  
Purchase period                     6 months  
Common stock purchased by employees                     150,677 130,512
Common stock purchased under purchase plan at average price                     $ 1.18 $ 1.03
Amount withheld by plan participants to purchase stock                     100,000,000  
Discount available to eligible employees related to employee stock purchase plan                     85.00%  
Shares authorized and available for issuance under the ESPP                     303,141  
Stock based compensation expenses 3,010,000 1,039,000 803,000 2,800,000 1,000,000 800,000            
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans 8,600,000                      
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans, period for recognition 2 years 7 months 6 days                      
Non-employees stock-based compensation expense $ 200,000 $ 100,000 $ 37,000