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Estimated Fair Value of Options on Dates of Each Grant Using Binomial Option Pricing Model (Detail)
12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.73% 0.82%  
Risk-free interest rate, lower range 7.71% 8.42% 8.21%
Risk-free interest rate, upper range 8.07% 8.63% 9.08%
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield     0.81%
Expected volatility 23.29% 24.30% 28.57%
Expected term (in years) 4 years 2 months 16 days 4 years 1 month 17 days 3 years 9 months 22 days
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield     0.83%
Expected volatility 26.46% 32.00% 41.52%
Expected term (in years) 5 years 7 months 28 days 5 years 5 months 12 days 5 years 5 months 9 days