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Stock-Based Compensation Plans (Details Textuals) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
|---|---|---|---|
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May 31, 2013
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May 31, 2012
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May 31, 2011
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| Stock Based Compensation Plans (Textual) [Abstract] | |||
| Number of shares authorized for issuance under stock plan | 39.1 | ||
| Shares available for future grants | 22.0 | ||
| Stock-based compensation costs | $ 22.8 | $ 22.9 | $ 24.8 |
| Income tax benefits | 8.5 | 8.3 | 8.4 |
| Total unrecognized compensation costs related to all unvested stock-based awards | $ 47.1 | ||
| Weighted-average period in years of all unvested stock-based awards | 2 years 10 months 25 days | ||
| No days service to be eligible for new hire grant, Non-management employee | 90 days | ||
| Contractual life of stock option grants | 10 years | ||
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Officers And Employees Nonqualified Stock Options Granted Prior To July Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | 20% per annum | ||
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Board Nonqualified Stock Options Granted Prior To October Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | one-third per annum | ||
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Officers Nonqualified Stock Options Granted Beginning In July Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | 25% per annum | ||
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Board Nonqualified Stock Options Granted Beginning In October Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | after one-year | ||
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Performance Stock Options [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | The awards will vest in full if performance targets for the fiscal year ending May 31, 2016 are achieved. Acceleration of vesting for up to one-half of the award will occur if performance targets for the fiscal year ending May 31, 2014 are achieved. There also is an opportunity to vest in one-half of the award at threshold performance, which is 95% of target. | ||
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Restricted Stock Unit [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | 20% per annum over five years with a small population of awards vesting on the fourth anniversary of the grant date | ||
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Officers Restricted Stock Awards Granted Prior To July Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | fifth anniversary | ||
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Officers Restricted Stock Awards Granted Beginning In July Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | one-third per annum | ||
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Board Restricted Stock Awards Granted Prior To October Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | third anniversary | ||
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Board Restricted Stock Awards Granted Beginning In October Two Zero One Zero [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | one-year anniversary | ||
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Unearned Performance Shares [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Vesting schedule | one year | ||
| Performance period for unearned performance shares | 2 years | ||