Benefit Plans (Details) $ in Thousands	12 Months Ended
Apr. 30, 2016 USD ($) employee executive shares	Apr. 30, 2015 USD ($) shares	Apr. 30, 2014 USD ($)
401(K) Plan
Defined Contribution Plan Disclosure
Employer discretionary contribution	$ 6,560	$ 5,852	$ 5,348
Common stock held by trustee of the 401K plan (shares) \| shares	1,419,841	1,453,251
Supplemental Executive 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	$ 5,230	$ 5,626
Discount rate	3.80%	4.00%
Pension and post-retirement expense incurred	$ 230	$ 326	93
Expected future payments, 2017	625
Expected future payments, 2018	625
Expected future payments, 2019	625
Expected future payments, 2020	625
Expected future payments, 2021	625
Other Post-Employment Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block
Expected future payments, 2017	507
Expected future payments, 2018	507
Expected future payments, 2019	457
Expected future payments, 2020	432
Expected future payments, 2021	$ 432
Number of individuals with deferred compensation agreements \| employee	3
Accrued deferred compensation liability	$ 4,043	3,960
Deferred compensation expense incurred	$ 238	$ 219	$ 156

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

+ References

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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

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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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20028-108363

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 25
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=6409733&loc=d3e19512-108361

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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

The interest rate used to adjust for the time value of money for the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References