Benefit Plans (Details) $ in Thousands	12 Months Ended
	Apr. 30, 2019 USD ($) employee executive shares	Apr. 30, 2018 USD ($) shares	Apr. 30, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Number of individuals with deferred compensation agreements | employee	2
Accrued deferred compensation liability	$ 2,870	$ 3,431
Expected future payments, 2020	401
Expected future payments, 2021	401
Expected future payments, 2022	401
Expected future payments, 2023	401
Expected future payments, 2024	401
Deferred compensation expense incurred	(97)	131	$ 370
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Employer discretionary contribution	$ 9,918	$ 9,614	8,181
Common stock held by trustee of the 401K plan (shares) | shares	1,261,258	1,389,694
Supplemental Employee Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Number of executives covered under SERP | executive	2
Annual benefit amount (percent of base compensation)	50.00%
Duration of benefits	20 years
Accrued deferred compensation liability	$ 3,800	$ 4,214
Discount rate		4.50%
Pension and post-retirement expense incurred	221	$ 112	$ 131
Expected future payments, 2020	635
Expected future payments, 2021	635
Expected future payments, 2022	635
Expected future payments, 2023	635
Expected future payments, 2024	$ 354
Minimum | Supplemental Employee Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Discount rate	3.78%
Maximum | Supplemental Employee Retirement Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Discount rate	4.01%