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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Jul. 31, 2011
Accounting Policies [Abstract] |
Assumptions for Black-Scholes Merton (BSM) option-pricing model |
|  |  |  | July 31, 2011 |  | July 31, 2010 |  | July 31, 2009
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Expected life (in years) |  |  |  |  | 5.3 – 6.8 |  |  |  | 5.2 – 7.1 |  |  |  | 5.2 – 7.1 |
Risk-free interest rate |  |  |  |  | 1.7 – 2.9 | % |  |  | 2.1 – 3.3 | % |  |  | 1.4 – 3.1 | %
Estimated volatility |  |  |  |  | 26 – 31 | % |  |  | 28 – 36 | % |  |  | 33 – 37 | %
Expected dividends |  |  |  |  | 0 | % |  |  | 0 | % |  |  | 0 | %
Weighted-average fair value at measurement date |  |  |  | $ | 13.40 |  |  | $ | 13.21 |  |  | $ | 13.09 |

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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Topic 718 -SubTopic 10 -Publisher FASB -Number -Article -Subparagraph (f)(2) -Name Accounting Standards Codification -Paragraph 2 -Section 50 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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