Stock-based Employee Compensation, Stock Option Plans, and Deferred Compensation Plan for Directors - Stock Options Issued (Details)	9 Months Ended
Sep. 30, 2019 $ / shares
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 45.11
Directors \| 5/11/2018
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 49.46
Volatility (percentage)	0.192
Expected life (years)	5 years
Assumed yield (percentage)	3.70%
Risk-free rate (percentage)	2.84%
Directors \| 5/3/2019
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 55.71
Volatility (percentage)	0.236
Expected life (years)	5 years
Assumed yield (percentage)	3.75%
Risk-free rate (percentage)	2.33%
Officers \| 5/11/2018
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 49.46
Volatility (percentage)	0.177
Expected life (years)	7 years
Assumed yield (percentage)	3.75%
Risk-free rate (percentage)	2.94%
Officers \| 5/3/2019
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 55.71
Volatility (percentage)	0.206
Expected life (years)	7 years
Assumed yield (percentage)	3.80%
Risk-free rate (percentage)	2.43%

Share Based Compensation Arrangement by Share Based Payment Award, Fair Value Assumptions, Volatility

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- Definition

Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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