Reconciliation of Weighted Average Shares Outstanding and Share Repurchases (Details) - shares	3 Months Ended	9 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Reconciliation of Weighted Average Shares Outstanding and Share Repurchases [Abstract]
Weighted average shares outstanding (in shares)	57,200,000	57,170,000	57,383,000	57,123,000
Less: Unvested restricted shares (in shares)	(42,000)	(135,000)	(53,000)	(144,000)
Shares used for basic earnings per share (in shares)	57,158,000	57,035,000	57,330,000	56,979,000
Dilutive effect of stock options and other stock awards (in shares)	468,000	836,000	552,000	757,000
Shares used for diluted earnings per share (in shares)	57,626,000	57,871,000	57,882,000	57,736,000
Stock Options [Member] \| Class A Common [Member]
Reconciliation of Weighted Average Shares Outstanding and Share Repurchases [Abstract]
Anti-dilutive shares excluded from diluted EPS calculation (in shares)	154,385	0	154,385	255,187
Warrants [Member]
Reconciliation of Weighted Average Shares Outstanding and Share Repurchases [Abstract]
Warrants issued during period (in shares)		0		0
Warrants [Member] \| Class A Common [Member]
Reconciliation of Weighted Average Shares Outstanding and Share Repurchases [Abstract]
Anti-dilutive shares excluded from diluted EPS calculation (in shares)	470,000		158,148
Restricted Stock [Member]
Reconciliation of Weighted Average Shares Outstanding and Share Repurchases [Abstract]
Anti-dilutive shares excluded from diluted EPS calculation (in shares)	0	0	0	26,740

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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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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.

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The number of warrants issued as [noncash or part noncash] consideration for a business or asset acquired. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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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.

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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).

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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.

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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.

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