Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2015	Apr. 30, 2014
Schedule Of Marketable Securities [Line Items]
Proceeds from sales/maturities of available-for-sale securities		$ 5,000	$ 33,300
Trading securities	[1],[2]	131,399	116,207
Gross unrealized gains		8,300	9,200
Gross unrealized losses		$ 200	$ 700
Minimum
Schedule Of Marketable Securities [Line Items]
Available-for-sale marketable securities, remaining maturities		1 month
Maximum
Schedule Of Marketable Securities [Line Items]
Available-for-sale marketable securities, remaining maturities		8 months

[1] The Company's financial assets measured at fair value on a recurring basis include trading securities classified as Level 1 and available-for-sale securities classified as Level 2. As of April 30, 2015 and 2014, the Company had no investments classified as Level 3.

[2] These investments are held in trust for settlement of the Company's vested and unvested obligations of $129.1 million and $117.6 million as of April 30, 2015 and 2014, respectively, under the ECAP (see Note 6 - Deferred Compensation and Retirement Plans). During fiscal 2015, 2014 and 2013, the fair value of the investments increased; therefore, the Company recognized income of $8.8 million, $9.5 million, and $7.6 million, respectively, which was recorded in other income, net.