Summary of Marketable Securities (Parenthetical) (Detail) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Oct. 31, 2015 |
Oct. 31, 2014 |
Oct. 31, 2015 |
Oct. 31, 2014 |
Apr. 30, 2015 |
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| Schedule Of Marketable Securities [Line Items] | |||||
| Obligations for which assets are held in trust | $ 140,900 | $ 140,900 | $ 129,100 | ||
| Gain (loss) on marketable securities | $ (2,500) | $ 2,500 | $ (1,818) | $ 4,527 | |
| X | ||||||||||
- Definition Schedule Of Marketable Securities [Line Items] No definition available.
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition Aggregate carrying value as of the balance sheet date of the liabilities for deferred compensation arrangements other than those specified elsewhere in the taxonomy. No definition available.
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