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Description of the Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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May. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Schedule of assumptions used in valuation of share-based compensation awards | The table set forth below provides the estimated fair value of options granted by the Company during fiscal years 2015, 2014 and 2013 and the significant weighted average assumptions used in determining such fair value under the Black-Scholes option- pricing model. The average expected life represents an estimate of the period of time stock options are expected to remain outstanding based on the historical exercise behavior of the option grantees. The risk-free interest rate was based on the U.S. Treasury yield curve corresponding to the expected life in effect at the time of the grant. The volatility was estimated based on historical volatility corresponding to the expected life.
| 2015 |  | 2014 |  | 2013
Estimated fair value of stock options granted | $ | 11.41 |  |  | $ | 10.37 |  |  | $ | 9.77 |
Assumptions: |  |  |  |  |  |  |  |
Expected dividend yield | 1.8 | % |  | 1.7 | % |  | 1.6 | %
Expected stock price volatility | 38.2 | % |  | 38.6 | % |  | 37.5 | %
Risk-free interest rate | 2.2 | % |  | 2.2 | % |  | 0.9 | %
Expected life of options | 6 years |  |  | 6 years |  |  | 6 years |

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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