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Number of share options and Stock Appreciation Rights (SARS) exercised during the current period.

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Face amount or stated value per share of common stock.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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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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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross 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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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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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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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Stock Compensation Plans - Omnibus Plan (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2013	Dec. 31, 2004
Stock Compensation Plans
Par value of shares of common stock (in dollars per share)	$ 0.01	$ 0.01
Stock-based compensation expense and related income tax benefits
Stock-based compensation expense	$ 4.0	$ 6.4	$ 5.8
Income tax benefit	(1.0)	(2.5)	(2.2)
Stock-based compensation, net of income tax benefit	3.0	3.9	3.6
Compensation costs related to equity awards and amounts recognized
Compensation expense recognized	$ (4.0)	(6.4)	$ (5.8)
Stock options awarded
Nonqualified stock options granted (in shares)	108,420
Per share weighted-average grant date fair value (in dollars per share)	$ 15.00
Number of Stock Options
Add: Options granted (in shares)	108,420
Stock Options
Stock Compensation Plans
Expiration period					10 years
Vesting period					3 years
Stock-based compensation expense and related income tax benefits
Stock-based compensation expense	$ 1.5
Compensation costs related to equity awards and amounts recognized
Unrecognized compensation cost at the beginning of the period	0.6
Grant date fair value current year grants	1.5
Compensation expense recognized	(1.5)
Unrecognized compensation cost at the end of the period	$ 0.6	0.6
Expected amortization period	1 year 8 months 12 days
Performance Shares and RSUs
Stock-based compensation expense and related income tax benefits
Stock-based compensation expense	$ 2.5
Compensation costs related to equity awards and amounts recognized
Unrecognized compensation cost at the beginning of the period	2.3
Grant date fair value current year grants	2.3
Compensation expense recognized	(2.5)
Unrecognized compensation cost at the end of the period	$ 2.1	$ 2.3
Expected amortization period	1 year 6 months
Options
Fair value assumptions
Expected term in years	5 years 8 months 6 days	5 years 9 months 6 days	5 years 9 months 6 days
Risk free interest rate (as a percent)	2.50%	2.10%	1.80%
Volatility (as a percent)	21.50%	22.90%	32.10%
Dividend yield (as a percent)	3.00%	3.00%	3.00%
Nonqualified stock options
Stock options awarded
Nonqualified stock options granted (in shares)	108,420	144,089	113,935
Per share weighted-average exercise price (in dollars per share)	$ 93.22	$ 82.11	$ 58.03
Per share weighted-average grant date fair value (in dollars per share)	$ 15.00	$ 13.54	$ 13.51
Number of Stock Options
Add: Options granted (in shares)	108,420	144,089	113,935
Weighted-Average Exercise Price
Add: Options granted (in dollars per share)	$ 93.22	$ 82.11	$ 58.03
RSUs \| Non-employee members of the board of directors
Stock Compensation Plans
Vesting period	1 year
Omnibus Plan
Stock Compensation Plans
Shares of common stock reserved for future issuance					3,500,000
Par value of shares of common stock (in dollars per share)					$ 0.01
Stock options awarded
Nonqualified stock options granted (in shares)	108,420
Per share weighted-average exercise price (in dollars per share)	$ 93.22
Number of Stock Options
Options outstanding at the beginning of the period (in shares)	464,958
Add: Options granted (in shares)	108,420
Less: Options exercised (in shares)	104,771
Less: Options forfeited/cancelled (in shares)	17,526
Options outstanding at the end of the period (in shares)	451,081	464,958
Weighted-Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)	$ 55.60
Add: Options granted (in dollars per share)	93.22
Less: Options exercised (in dollars per share)	38.73
Less: Options forfeited/cancelled (in dollars per share)	83.89
Options outstanding at the end of the period (in dollars per share)	$ 67.46	$ 55.60
2013 Omnibus Plan
Stock Compensation Plans
Shares of common stock reserved for future issuance	1,260,000
Additional common stock reserved for issuance subject to shareholders approval (in shares)				800,000
Reduction in number of shares available for future issuance (in shares)	174,000