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Computation of Earnings Per Common Share - Narratives (Details) - $ / shares | Jul. 28, 2018 | Apr. 28, 2018 | Sep. 15, 2015
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Convertible Note Hedge |  |  |
Shares used in computing earnings per common share: |  |  |
Debt instrument, convertible, conversion price (per share) | $ 96.89 |  | $ 96.89
0.75% Convertible Senior Notes Due 2021 |  |  |
Shares used in computing earnings per common share: |  |  |
Debt, interest rate (in percent) | 0.75% |  |
Debt instrument, convertible, conversion price (per share) |  |  | 96.89
Class of warrant or right, exercise price of warrants or rights (per warrant) | $ 130.43 |  | $ 130.43
Weighted Average | 0.75% Convertible Senior Notes Due 2021 |  |  |
Shares used in computing earnings per common share: |  |  |
Share price (usd per share) | $ 99.27 | $ 110.46 |

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