Benefit Plans (Details) $ in Thousands	12 Months Ended
Apr. 30, 2018 USD ($) employee executive shares	Apr. 30, 2017 USD ($) shares	Apr. 30, 2016 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Number of individuals with deferred compensation agreements \| employee	3
Accrued deferred compensation liability	$ 3,431	$ 3,825
Expected future payments, 2019	464
Expected future payments, 2020	439
Expected future payments, 2021	439
Expected future payments, 2022	439
Expected future payments, 2023	439
Deferred compensation expense incurred	131	370	$ 238
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Employer discretionary contribution	$ 9,614	$ 8,181	6,560
Common stock held by trustee of the 401K plan (shares) \| shares	1,389,694	1,401,764
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	$ 4,214	$ 4,737
Discount rate	4.50%	4.00%
Pension and post-retirement expense incurred	$ 112	$ 131	$ 230
Expected future payments, 2019	635
Expected future payments, 2020	625
Expected future payments, 2021	625
Expected future payments, 2022	625
Expected future payments, 2023	$ 625

Deferred Compensation Arrangement With Individual, Number of Individuals Covered Under Plan

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- Definition

Defined Benefit Plan, Annual Retirement Benefit, Percentage

+ References

No definition available.

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- Definition

Defined Benefit Plan, Duration Of Benefits

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No definition available.

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- Definition

Defined Benefit Plans, Non-Qualified Supplemental Executive Plan, Number of Executives Covered

+ References

No definition available.

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
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- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable within one year (or the operating cycle, if longer). Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
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- Definition

Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

+ References