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Fair Value of Employee Stock Options Assumptions (Detail)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]      
Risk free interest rate, minimum 1.61% 1.64% 0.94%
Risk free interest rate, maximum 1.86% 2.11% 1.82%
Volatility, minimum 69.76% 73.98% 75.83%
Volatility, maximum 71.84% 84.85% 86.26%
Dividends 0.00% 0.00% 0.00%
Minimum      
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]      
Expected lives 5 years 9 months 15 days 5 years 9 months 7 days 2 years 7 months 21 days
Maximum      
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]      
Expected lives 5 years 10 months 10 days 6 years 1 month 2 days 5 years 9 months 7 days