Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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 estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Net number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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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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Percent of an employee's targeted award to be paid out, Maximum.

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Percent of an employee's targeted award to be paid out, Minimum.

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Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance under the 2016 Plan (in shares)	2,484,562		2,484,562
Stock options, granted (in shares)			157,416
Stock options, weighted average exercise price (in dollars per share)			$ 275.02
Stock options, weighted average grant date fair value (in dollars per share)			$ 63.19
Risk-free interest rate (in hundredths)			0.70%
Expected life (in years)			5 years 7 months 6 days
Stock volatility (in hundredths)			23.90%
Dividend yield (in hundredths)			0.30%
Stock-based compensation expense	$ 10.3	$ 12.3	$ 16.2	$ 17.7
Performance Share Unit (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			36,174
Grant date fair value (in dollars per share)			$ 329.88
PSU payout, minimum (in hundredths)	0.00%		0.00%
PSU payout, maximum (in hundredths)	200.00%		200.00%
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			4,637
Grant date fair value (in dollars per share)			$ 279.92