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Changes in Each Component of Accumulated Other Comprehensive (Loss) Income (Parenthetical) (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Apr. 30, 2017 | Apr. 30, 2016 | Apr. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Tax effect on reclassifications of realized net losses | $ 1,200 | $ 1,100 | $ 1,200
Tax effects on unrealized (losses) gains | 1,900 | $ (2,300) | $ (2,300)
Tax effect on unrealized (losses) | $ (406) |  |

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- Definition Amount of tax (expense) benefit, before reclassification adjustments, related to (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580 + Details
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- Definition Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans. + References No definition available. + Details
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- Definition Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580 + Details
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