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, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 944,000 $ 292,000 $ 2,087,000 $ 743,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans 9,400,000   9,400,000  
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the stock option plans, period for recognition     2 years 9 months 18 days  
Non-employee stock-based compensation expense 100,000 20,000 200,000 51,000
Total intrinsic value of stock options exercised     1,400,000 6,000.0
Cash received from stock option exercises     400,000 14,000.0
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 540,784   540,784  
Employee Stock-Based Compensation Expense [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense 800,000 300,000 1,900,000 700,000
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 303,141   303,141  
Plan participants purchased shares     150,677  
Average purchase price under 2004 Employee Stock Purchase Plan $ 1.18   $ 1.18  
Other Comprehensive Loss [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 900,000 $ 300,000 $ 2,100,000 $ 700,000