Share-Based Payments (Details 3) - $ / shares	12 Months Ended
Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Restricted Shares And Deferred Stock Units [Member]
Weighted-average grant date fair values of the equity awards
Granted Restricted Shares and Deferred Stock Units and Performance Units	136,127	180,997	97,922
Granted Weighted Average Grant Date Fair Value (in dollars per share)	$ 126.80	$ 133.92	$ 113.57
Performance Units [Member]
Weighted-average grant date fair values of the equity awards
Granted Restricted Shares and Deferred Stock Units and Performance Units	84,051	73,701	121,936
Granted Weighted Average Grant Date Fair Value (in dollars per share)	$ 103.86
Granted Weighted Average Conversion Date Fair Value (in dollars per share)	$ 103.86	$ 126.80	$ 132.46

The weighted average fair value for nonvested equity-based awards issued during the period on other than stock (or unit) options plans.

No definition available.

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- Definition

Weighted average grant date fair values of equity.

+ 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 at grant date for nonvested equity-based awards issued 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

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