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Fair Value of Options, Black-Scholes Model Assumptions (Detail)
12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Mar. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield    0.00% 0.00%
Risk free interest rates, minimum   1.23% 2.04%
Risk free interest rates, maximum   2.84% 2.77%
Risk free interest rates         
Expected volatility, minimum   78.36% 75.88%
Expected volatility, maximum   81.98% 77.61%
Expected volatility         
Minimum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term   5 years 6 months 5 years 6 months
Maximum
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term   7 years 7 years