Deferred Compensation and Retirement Plans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013	Apr. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	$ 167,000,000		$ 167,000,000		$ 159,200,000
Outstanding policy loans	73,300,000		73,300,000		73,300,000
Increase in market value of the underlying COLI investments	1,800,000	2,000,000	6,432,000	4,236,000
Increase in fair value trading securities	1,200,000	3,800,000	7,578,000	4,927,000
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Company's contributions	400,000	700,000	17,100,000	20,000,000
Deferred compensation arrangement vesting terms	Participants generally vest in Company contributions over a four year period.
Increase (decrease) in compensation expense	$ 1,100,000	$ 2,900,000	$ 6,100,000	$ 3,400,000