Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Apr. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in market value of the underlying COLI investments			$ 3,316	$ 1,801
Recognized investment income(expense)	$ 3,900	$ (7,100)	7,090	(8,904)
CSV of COLI Contracts
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	180,300		180,300		$ 175,700
Outstanding policy loans	68,400		68,400		$ 68,400
Increase (decrease) in market value of the underlying COLI investments	100	(1,500)	3,300	1,800
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
(Loss) gain on deferred compensation plan	$ 4,100	$ (5,300)	$ 6,700	$ (6,200)
Executive Capital Accumulation Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation arrangement vesting period			4 years
Executive Capital Accumulation Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation arrangement vesting period			5 years