Reconciliation of Weighted Average Shares Outstanding (Details) - shares	12 Months Ended
Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Reconciliation of Weighted Average Shares Outstanding [Abstract]
Weighted Average Shares Outstanding (in shares)	57,181,000	57,531,000	58,253,000
Less: Unvested restricted shares (in shares)	(138,000)	(194,000)	(255,000)
Shares Used for Basic Earnings Per Share (in shares)	57,043,000	57,337,000	57,998,000
Dilutive Effect of Stock Options and Other Stock Awards (in shares)	845,000	862,000	736,000
Shares Used for Diluted Earnings Per Share (in shares)	57,888,000	58,199,000	58,734,000
Stock Options [Member] \| Common Stock Class A [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from diluted EPS calculation (in shares)	244,590	301,527	336,803
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded from diluted EPS calculation (in shares)	26,740	0	15,200

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1500-109256

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- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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This element represents the weighted average total number of shares issued throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period before considering any reductions (for instance, shares held in treasury) to arrive at the weighted average number of shares outstanding. Weighted average relates to the portion of time within a reporting period that common shares have been issued and outstanding to the total time in that period. Such concept is used in determining the weighted average number of shares outstanding for purposes of calculating earnings per share (basic).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

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Number of shares of restricted stock determined by relating the portion of time within a reporting period that restricted shares have been outstanding to the total time in that period. Restricted shares are subject to sales, contractual, regulatory or other restrictions that prevent or inhibit the holder from freely disposing of them before the restriction ends.

+ References

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