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

No definition available.

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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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No definition available.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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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.

+ References

No definition available.

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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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Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

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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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No definition available.

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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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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) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	$ 45,200
Weighted average recognition period for unrecognized compensation expense, in years	1 year 7 months 6 days
Intrinsic value of stock options exercised	$ 78,300	$ 51,000	$ 35,100
Number of unissued shares of common stock each DSU represents right to receive	1
Share-based compensation expense	$ 23,517	$ 19,891	$ 19,884
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years	7 years
Deferred stock units, outstanding	229,000	231,000
2009 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under share-based incentive plans	19,900,000
Shares available for grant under share-based incentive plans	11,400,000
1997 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under share-based incentive plans	4,700,000
Shares available for grant under share-based incentive plans	1,200,000
Common stock issued in connection with the Employee Stock Purchase Plan	61,000	85,000	105,000
Discount from market value for employee stock purchase rights	15.00%
Stock Options Granted To Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Restricted Stock Units Granted To Employees With Ratable Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
Restricted Stock Units Granted To Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of unvested share-based awards to vest upon change in control	25 percent
Fair value of awards vested during period	$ 22,100	$ 12,400	$ 15,300
Deferred Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred stock units, outstanding	229,000	231,000
Stock Options And Stock Appreciation Rights [Member]
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 to 1
Awards Other Than Stock Options And Stock Appreciation Rights [Member]
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 to 1
Stock Options Granted To Employees With Ratable Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of unvested share-based awards to vest upon change in control	25
Fair value of options vested during period	$ 9,200	$ 9,300	$ 8,700