Stock-Based Compensation, President and CEO New Hire Equity Awards (Details) $ / shares in Units, $ in Millions	12 Months Ended
Apr. 30, 2018 USD ($) Installment $ / shares shares
ELTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Targeted long-term incentive as percentage of base salary	300.00%
Targeted long-term incentive value \| $	$ 2.7
ELTIP [Member] \| Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of targeted long-term incentive value	60.00%
Grant date fair value (in dollars per share) \| $ / shares	$ 59.15
Awards granted (in shares) \| shares	30,916
ELTIP [Member] \| Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of targeted long-term incentive value	40.00%
Grant date fair value (in dollars per share) \| $ / shares	$ 59.15
Awards granted (in shares) \| shares	20,611
ELTIP [Member] \| Restricted Share Units [Member] \| Vesting on April 30, 2018 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards vesting percentage	25.00%
ELTIP [Member] \| Restricted Share Units [Member] \| Vesting on April 30, 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards vesting percentage	25.00%
ELTIP [Member] \| Restricted Share Units [Member] \| Vesting on April 30, 2020 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards vesting percentage	25.00%
ELTIP [Member] \| Restricted Share Units [Member] \| Vesting on April 30, 2021 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards vesting percentage	25.00%
Sign-On Grant [Member] \| Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value (in dollars per share) \| $ / shares	$ 59.15
Awards granted (in shares) \| shares	67,625
Grant value \| $	$ 4.0
Number of equal installments \| Installment	2

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- Definition

Refers to the percentage of targeted long-term incentive value.

+ References

No definition available.

+ Details

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- Definition

Refers to the targeted long-term incentive of share-based compensation awards as a percentage of base salary during the performance cycle.

+ References

No definition available.

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- Definition

Refers to the value of base salary for targeted long-term incentive of share-based compensation awards.

+ References

No definition available.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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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No definition available.

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- Definition

Percentage of vesting of share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Value, before forfeitures, of stock or other type of equity granted of any equity-based compensation plan other than an employee stock ownership plan (ESOP).

+ References

No definition available.

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