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Amortized Cost and Fair Values of Marketable Securities Classified as Available-For-Sale Investments (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified | Oct. 31, 2013 | Apr. 30, 2013
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Schedule of Available-for-sale Securities [Line Items] |  |
Marketable securities that have been in a continuous unrealized loss position for 12 months or more | $ 0 | $ 0

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- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Balance Type: | na
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