Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Additional Information (Detail)

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Stock Based Compensation - Additional Information (Detail) (USD $)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense $ 1,053,000 $ 398,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans 13,200,000  
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans, period for recognition 2 years 10 months 24 days  
Non-employee stock-based compensation expense 35,000 100,000
Total intrinsic value of stock options exercised 100,000 400,000
Cash received from stock option exercises 33,000 200,000
Amount withheld by plan participants to purchase stock 100,000  
2004 Equity Incentive Plan [Member]
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Additional shares authorized for issuance 1,250,000  
Shares authorized and available for issuance 341,369  
Employee stock-based compensation expense [Member]
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock-based compensation expense $ 1,000,000 $ 300,000
2004 Employee Stock Purchase Plan [Member]
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Additional shares authorized for issuance 100,000  
Shares authorized and available for issuance 322,966  
Plan participants purchased shares 80,175  
Average purchase price under 2004 Employee Stock Purchase Plan $ 1.55