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 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 1,231,000 $ 944,000 $ 3,556,000 $ 2,087,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans 11,600,000   11,600,000  
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans, period for recognition     2 years 6 months  
Non-employee stock-based compensation expense 36,000 100,000 100,000 200,000
Total intrinsic value of stock options exercised     500,000 1,400,000
Cash received from stock option exercises     200,000 400,000
Amount withheld by plan participants to purchase stock 100,000   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 160,214   160,214  
Employee stock-based compensation expense [Member]
        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 1,200,000 $ 800,000 $ 3,500,000 $ 1,900,000
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 235,896   235,896  
Plan participants purchased shares     167,245  
Average purchase price under 2004 Employee Stock Purchase Plan $ 1.69   $ 1.69