| **Earnings Per Share (Details) (USD $)In Thousands, except Per Share data, unless otherwise specified** | 3 Months Ended                                                                | 6 Months Ended                                                                |
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| **Earnings Per Share [Abstract]**                                                                       |                                                                          |                                                                          |   |   |
| Net Income                                                                                              | $ 66,402us-gaap_NetIncomeLoss                                                 | $ 62,540us-gaap_NetIncomeLoss                                                 | $ 159,380us-gaap_NetIncomeLoss | $ 160,112us-gaap_NetIncomeLoss |
| Average shares of common stock outstanding for basic earnings per share                                 | 78,818us-gaap_WeightedAverageNumberOfSharesOutstandingBasic                   | 77,982us-gaap_WeightedAverageNumberOfSharesOutstandingBasic                   | 78,717us-gaap_WeightedAverageNumberOfSharesOutstandingBasic | 77,477us-gaap_WeightedAverageNumberOfSharesOutstandingBasic |
| Contingently issuable shares under incentive compensation plans                                         | 279us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements | 309us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements | 302us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements | 325us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements |
| Contingently issuable shares under forward sale agreement                                               | 18us-gaap_IncrementalCommonSharesAttributableToEquityForwardAgreements        |                                                                          | 29us-gaap_IncrementalCommonSharesAttributableToEquityForwardAgreements |   |
| Average shares of dilutive stock                                                                        | 79,115us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding                 | 78,291us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding                 | 79,048us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding | 77,802us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding |
| Basic (usd per share)                                                                                   | $ 0.84us-gaap_EarningsPerShareBasic                                           | $ 0.80us-gaap_EarningsPerShareBasic                                           | $ 2.02us-gaap_EarningsPerShareBasic | $ 2.07us-gaap_EarningsPerShareBasic |
| Diluted (usd per share)                                                                                 | $ 0.84us-gaap_EarningsPerShareDiluted                                         | $ 0.80us-gaap_EarningsPerShareDiluted                                         | $ 2.02us-gaap_EarningsPerShareDiluted | $ 2.06us-gaap_EarningsPerShareDiluted |

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| - Definition
The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.
+ References
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| - Definition
The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.
+ References
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| - Definition
Additional shared included in the calculation of diluted EPS as a result of the potentially dilutive effect of equity forward arrangements using the reverse treasury stock method.
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| - Definition
Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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| - Definition
The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.
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| - Definition
Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.
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