The number of unissued shares of common stock that each DSU represents the right to receive.

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The ratio of the number of shares issued under share-based awards to the number of shares authorized under stock plans.

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Total number of shares of other common stock instruments held by shareholders, such as exchangeable shares. May be all or portion of the number of common shares authorized.

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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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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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Discount rate from fair value on offering date that participants pay for shares.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Percentage of vesting of share-based compensation awards.

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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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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Share-Based Compensation (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, net of estimated forfeitures, for unvested share-based compensation awards outstanding \| $	$ 51.2
Weighted average recognition period for unrecognized compensation expense, in years	1 year 8 months 12 days
Intrinsic value of stock options exercised \| $	$ 87.1	$ 78.3	$ 51.0
Number of unissued shares of common stock each DSU represents right to receive (in shares)	1
Deferred stock units, outstanding (in shares)	162,000	229,000
2018 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under share-based incentive plans (in shares)	7,500,000
Shares available for grant under share-based incentive plans (in shares)	7,200,000
Stock options and stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ratio of shares issued under share-based awards to shares authorized under stock plans	1
Awards other than stock options and stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ratio of shares issued under share-based awards to shares authorized under stock plans	2.4
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of options vested during period \| $	$ 10.5	$ 9.2	9.3
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
Restricted stock units granted to employees with ratable vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
Restricted stock units (RSU's)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested during period \| $	$ 24.5	$ 22.1	$ 12.4
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
Deferred Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred stock units, outstanding (in shares)	162,000	229,000
1997 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under share-based incentive plans (in shares)	4,700,000
Shares available for grant under share-based incentive plans (in shares)	1,200,000
Discount from market value for employee stock purchase rights	15.00%
Common stock issued in connection with the Employee Stock Purchase Plan (in shares)	52,000	61,000	85,000
Share-based Compensation Award, Tranche One \| Stock options granted to employees with ratable vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
Share-based Compensation Award, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term	10 years
Share-based Compensation Award, Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term	7 years