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Significant Assumptions Used to Determine Fair Value of Auction Rate Securities (Detail)
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Apr. 30, 2012
Year
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Oct. 31, 2011
Year
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|---|---|---|
| Schedule of Available-for-sale Securities [Line Items] | ||
| Yields | 2.15% | |
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Minimum
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Discount rates | 0.62% | 3.21% |
| Yields | 2.00% | 2.00% |
| Average expected lives | 4 | 4 |
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Maximum
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Discount rates | 4.47% | 17.50% |
| Yields | 3.50% | 3.50% |
| Average expected lives | 10 | 10 |