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Retirement Benefits - Summary of Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Apr. 30, 2018 | Apr. 30, 2017 | Apr. 30, 2016
Retirement Benefits [Abstract] |  |  |
Interest cost | $ 875 | $ 927 | $ 912
Expected return on plan assets | (1,314) | (1,244) | (1,363)
Recognition of net loss | 1,133 | 1,257 | 1,223
Net periodic pension cost | $ 694 | $ 940 | $ 772

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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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