Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans and Stock Based Compensation - Assumptions of Equity-Based Payments to Non-Employees (Detail)

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Equity Incentive Plans and Stock Based Compensation - Assumptions of Equity-Based Payments to Non-Employees (Detail) (Non-employee Stock-based Compensation Expense [Member])
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Non-employee Stock-based Compensation Expense [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 2.51% 1.93% 1.37%
Expected life (in years) 10 years 10 years 5 years 1 month 24 days
Dividend yield         
Expected volatility 100.00% 101.00% 92.00%