Marketable Securities - Additional Information (Detail) (USD $)	3 Months Ended
	Jul. 31, 2014		Jul. 31, 2013	Apr. 30, 2014
Schedule Of Marketable Securities [Line Items]
Proceeds from sales/maturities of available-for-sale securities	$ 2,000,000		$ 29,300,000
Trading securities	116,719,000	[1],[2]		116,207,000	[1],[2]
Gross unrealized gains	10,400,000			9,200,000
Gross unrealized losses	$ 500,000			$ 700,000
Minimum
Schedule Of Marketable Securities [Line Items]
Available-for-sale marketable securities, remaining maturities	5 months
Maximum
Schedule Of Marketable Securities [Line Items]
Available-for-sale marketable securities, remaining maturities	1 year 6 months

[1] These investments are held in trust for settlement of the Company's vested and unvested obligations of $118.2 million and $117.6 million as of July 31, 2014 and April 30, 2014, respectively, under the ECAP (see Note 6 - Deferred Compensation and Retirement Plans). During both the three months ended July 31, 2014 and 2013, the fair value of the investments increased; therefore, the Company recognized income of $2.0 million, which was recorded in other income, net.

[2] 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 July 31, 2014 and April 30, 2014, the Company had no investments classified as Level 3.