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Assumptions Used in Black-Scholes Pricing Model (Detail) - Stock Option Awards
3 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term of options in years 6 years 3 months 18 days 6 years 3 months 18 days
Expected volatility, minimum 33.20% 34.60%
Expected volatility, maximum 33.30% 34.90%
Risk-free interest rate, minimum 2.00% 2.70%
Risk-free interest rate, maximum 2.30% 2.80%
Expected dividend yield 0.00% 0.00%