Weighted Average Assumptions Used to Estimate Fair Value Each Option (Detail)	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	4.00%	4.00%	4.30%
Expected volatility	34.50%	47.60%	59.40%
Risk-free interest rate	1.70%	1.50%	0.70%
Expected term	5 years	5 years	4 years 3 months 18 days