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

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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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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for 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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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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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Number of shares authorized for issuance under share-based payment arrangement.

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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 award under share-based payment arrangement.

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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 Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 39,278	$ 25,157	$ 23,517
Income tax benefit resulting from share-based compensation expense		4,861	4,190	6,810
Unrecognized compensation expense, net of estimated forfeitures, for unvested share-based compensation awards outstanding	$ 50,100	$ 50,100
Weighted average recognition period for unrecognized compensation expense, in years		1 year 8 months 12 days
Intrinsic value of stock options exercised		$ 83,700	$ 87,100	78,300
Number of unissued shares of common stock each DSU represents right to receive (in shares)		1
Deferred stock units, outstanding (in shares) \| shares	143,000,000	143,000,000	162,000,000
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) \| shares			7,500,000
Shares available for grant under share-based incentive plans (in shares) \| shares	6,800,000	6,800,000
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]
Share-based compensation expense	$ 10,900
Income tax benefit resulting from share-based compensation expense	$ 800
Award vesting rights, percentage		25.00%
Fair value of options vested during period		$ 12,200	$ 10,500	9,200
Restricted stock units (RSU's)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights, percentage		25.00%
Fair value of awards vested during period		$ 23,800	$ 24,500	$ 22,100
Deferred Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred stock units, outstanding (in shares) \| shares	143,000	143,000	162,000
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) \| shares	4,700,000	4,700,000
Shares available for grant under share-based incentive plans (in shares) \| shares	1,100,000	1,100,000
Discount from market value for employee stock purchase rights		15.00%
Common stock issued in connection with the Employee Stock Purchase Plan (in shares) \| shares		47,000	52,000	61,000
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 One \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term		7 years
Share-based Compensation Award, Tranche One \| Restricted stock units 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 \| Stock options granted to employees with ratable vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Share-based Compensation Award, Tranche Two \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term		10 years
Share-based Compensation Award, Tranche Two \| Restricted stock units granted to employees with ratable vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years