Deferred Compensation and Retirement Plans - Additional Information (Detail) (USD $)	3 Months Ended
Jul. 31, 2012	Jul. 31, 2011	Apr. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Gross CSV of COLI contracts	$ 152,200,000		$ 151,100,000
Outstanding policy loan	73,300,000		73,300,000
Increased in market value of COLI investments	671,000	905,000
Company's contributions	17,500,000
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Company's contributions	17,500,000	12,300,000
Deferred compensation arrangement vesting terms	Participants generally vest in Company contributions over a four year period
Gain on investment	1,000,000	1,300,000
Deferred compensation arrangement, expected company contribution in remainder of fiscal year	$ 2,000,000

73,300,000

17,500,000

Participants generally vest in Company contributions over a four year period

$ 2,000,000