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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, 2017
Mar. 31, 2016
Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00% 0.73% 0.82%
Risk-free interest rate, lower range 0.00% 7.71% 8.42%
Risk-free interest rate, upper range 0.00% 8.07% 8.63%
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 0.00% 23.29% 24.30%
Expected term (in years)   4 years 2 months 16 days 4 years 1 month 16 days
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 0.00% 26.46% 32.00%
Expected term (in years)   5 years 7 months 28 days 5 years 5 months 12 days