Commitments And Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Commitments and Contingencies [Line Items]
Lease expiration date	2026
Total rental expense	$ 38.4	$ 35.5	$ 32.4
Maximum amount to be paid to the executive officers under absence of change of control	8.2
Maximum amount to be paid to the executive officers under change of control	$ 10.8
Employment agreements	The Company has a policy of entering into offer letters of employment or letters of promotion with vice presidents which provide for an annual base salary and discretionary and incentive bonus payments. Certain key vice presidents who typically have been employed by the Company for several years may also have a standard form employment agreement. In addition, the Company has a severance policy for all of its vice presidents that provides for minimum payments based on length of service. Upon termination without cause, the Company is required to pay the greater of the amount due under the employment agreement, if any, or the severance policy. The Company also requires its vice presidents to agree in their employment letters and their employment agreement, if applicable, not to compete with the Company both during the term of their employment, and for a period of up to two years after their employment ends. For a period of two years after their employment with the Company, former vice presidents are prohibited from soliciting employees of the Company for employment outside of the Company.