Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands |
3 Months Ended | ||||||
---|---|---|---|---|---|---|---|
Jul. 31, 2015 |
Jul. 31, 2014 |
Apr. 30, 2015 |
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Schedule Of Marketable Securities [Line Items] | |||||||
Proceeds from maturities of available-for-sale securities | $ 3,000 | $ 2,000 | |||||
Trading securities | [1],[2] | 127,793 | $ 131,399 | ||||
Gross unrealized gains | 8,000 | 8,300 | |||||
Gross unrealized losses | $ 600 | $ 200 | |||||
Minimum | |||||||
Schedule Of Marketable Securities [Line Items] | |||||||
Available-for-sale marketable securities, remaining maturities | 2 months | ||||||
Maximum | |||||||
Schedule Of Marketable Securities [Line Items] | |||||||
Available-for-sale marketable securities, remaining maturities | 5 months | ||||||
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