Deferred Compensation and Retirement Plans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Apr. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Increase in market value of the underlying COLI investments			$ 4,227	$ 3,172
Recognized investment income(expense)	$ 3,400	$ (700)	6,797	3,226
CSV of COLI Contracts
Defined Benefit Plan Disclosure [Line Items]
Gross CSV	182,500		182,500		$ 180,300
Outstanding policy loans	66,800		66,800		$ 67,200
Increase in market value of the underlying COLI investments	1,700	700	4,200	3,200
Executive Capital Accumulation Plan
Defined Benefit Plan Disclosure [Line Items]
Gain (loss) on deferred compensation plan	3,500	$ (600)	$ 7,200	$ 2,600
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
Defined Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected future employer contributions, current fiscal year	$ 200		$ 200