Stock-based Employee Compensation, Stock Option Plans, and Deferred Compensation Plan for Directors - Stock Options Issued (Details)	6 Months Ended
Jun. 30, 2020 $ / shares
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 49.19
Directors \| May 3, 2019
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 55.71
Volatility	0.236
Expected life (years)	5 years
Assumed yield	3.75%
Risk-free rate	2.33%
Directors \| April 24, 2020
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 50.00
Volatility	0.258
Expected life (years)	5 years
Assumed yield	3.80%
Risk-free rate	0.36%
Officers \| May 3, 2019
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 55.71
Volatility	0.206
Expected life (years)	7 years
Assumed yield	3.80%
Risk-free rate	2.43%
Officers \| April 24, 2020
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Exercise price (in usd per share)	$ 50.00
Volatility	0.240
Expected life (years)	7 years
Assumed yield	3.85%
Risk-free rate	0.51%

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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- Definition

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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