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Financial Instruments - Financial Instruments and Balance Sheet Classification (Parenthetical) (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Apr. 30, 2018 | Apr. 30, 2017 | Apr. 30, 2016
Investment Holdings [Line Items] |  |  |
Obligations for which assets are held in trust | $ 118,200 | $ 99,500 |
Gain (loss) on marketable securities | $ 10,278 | $ 10,842 | $ (3,333)

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- Definition This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(d)) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)(a)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(g)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition Amount of the liabilities for deferred compensation arrangements classified as other. + References No definition available. + Details
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