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Estimated Fair Value of Each Option Award at Grant Date by Using Black-Scholes Option Pricing Model (Detail)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Share Based Compensation [Line Items]    
Dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Expected volatility, in years 90.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate 90.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
Risk-free interest rates minimum 1.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum  
Expected lives, in years 5 years  
Maximum [Member]    
Share Based Compensation [Line Items]    
Risk-free interest rates maximum   2.80%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Expected lives, in years   10 years
Minimum [Member]    
Share Based Compensation [Line Items]    
Risk-free interest rates minimum   1.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Expected lives, in years   5 years