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 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 1,272,000 $ 744,000 $ 2,325,000 $ 1,143,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans 12,700,000   12,700,000  
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans, period for recognition     2 years 8 months 12 days  
Non-employee stock-based compensation expense 34,000 33,000 100,000 100,000
Total intrinsic value of stock options exercised     400,000 500,000
Cash received from stock option exercises     200,000 200,000
Amount withheld by plan participants to purchase stock 200,000   200,000  
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 181,369   181,369  
Employee stock-based compensation expense [Member]
        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 1,200,000 $ 700,000 $ 2,200,000 $ 1,000,000
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   322,966  
Plan participants purchased shares     80,175  
Average purchase price under 2004 Employee Stock Purchase Plan $ 1.55   $ 1.55