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Retirement Benefits - Summary of Plan Assets by Asset Categories (Detail) - USD ($) $ in Thousands | Apr. 30, 2017 | Apr. 30, 2016 | Apr. 30, 2015
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, Plan asset | $ 17,198 | $ 15,817 | $ 17,094
Defined benefit plan, Plan asset percentage | 100.00% | 100.00% |
Equity Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, Plan asset | $ 10,611 | $ 11,851 |
Defined benefit plan, Plan asset percentage | 62.00% | 75.00% |
Fixed Income Securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, Plan asset | $ 6,466 | $ 3,917 |
Defined benefit plan, Plan asset percentage | 37.00% | 25.00% |
Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, Plan asset | $ 121 | $ 49 |
Defined benefit plan, Plan asset percentage | 1.00% |  |

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- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=64937038&loc=d3e12355-114930 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Assets -URI http://asc.fasb.org/extlink&oid=6749337 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Plan Assets -URI http://asc.fasb.org/extlink&oid=6520858 + Details
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