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Share Based Compensation Arrangement By Employee Stock Purchase Plan Stock Purchases as Percentage Of Employee Compensation Maximum.

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Share based Compensation Arrangement by Share based Payment Award, Equity Instruments Other than Options, Granted in Period, Weighted Average Remaining Contractual Term.

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Share Based Compensation Arrangement By Share Based Payment Award Exercisable Price Percentage Of Closing Price Of Another Class Of Stock.

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Share based compensation arrangement by share based payment award expiry period from date of grant.

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Share Based Compensation Arrangement By Share Based Payment Award Maximum Share Value Authorized For Purchase Under Employee Stock Purchase Plan.

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Share-Based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Actual Performance Percentage

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Share-Based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Target Performance Percentage

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Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options, Outstanding, Intrinsic Value.

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Share based Compensation Arrangement by Share based Payment Award, Equity Instruments Other Than Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value.

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Face amount or stated value per share of common stock.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Unrecognized cost of unvested share-based compensation awards.

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-Name Accounting Standards Codification
-Topic 718
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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 cash inflow associated with the amount received from the stock plan during the period.

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-Name Accounting Standards Codification
-Topic 230
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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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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 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 number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Stock-Based Compensation (Details) - USD ($)	12 Months Ended
Stock-Based Compensation (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	5,700,000
Common stock par value (in Dollars per share)	$ 0.0005	$ 0.0005
Stock-based compensation expense	$ 78,943,000	$ 46,661,000	$ 46,149,000
Total share-based compensation cost not yet recognized	$ 79,900,000
Remaining weighted average service period	2 years 4 months 24 days
Weighted average remaining contractual term	1 year 2 months 12 days
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase plan, stock purchases as a percentage of employee compensation, maximum	10.00%
Maximum share value authorized for purchase under employee stock purchase plan	$ 23,750
Exercisable price percentage of closing price of another class of stock	95.00%
Maximum number of shares that may be purchased by eligible participants	800,000
Proceeds from stock grants	$ 11,700,000	9,300,000	7,500,000
Retirement Eligible Employees Equity Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 22,900,000	$ 19,400,000	$ 20,100,000
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted average service period	6 years 1 month 6 days
Award vesting period	4 years
Award expiry period from date of grant	7 years
Total compensation cost not yet recognized, period for recognition	4 years
Equity instruments number of shares unvested (in shares)	1,200,000	1,300,000
Aggregate intrinsic value of outstanding shares	$ 55,000,000
Aggregate intrinsic value of shares vested and exercisable	$ 30,200,000
Grants during period (in shares)	300,000
Stock Appreciation Rights (SARs) \| Unvested
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments number of shares unvested (in shares)	700,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments number of shares unvested (in shares)	1,500,000	1,300,000
Grants during period (in shares)	1,100,000
Restricted Stock Units (RSUs) \| CEB
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants during period (in shares)	600,000
Restricted Stock Units (RSUs) \| Service-based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Grants during period (in shares)	900,000
Restricted Stock Units (RSUs) \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants during period (in shares)	200,000
Performance share, actual yielded performance, percent	186.00%
Restricted Stock Units (RSUs) \| Performance Shares \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance shares, target performance percentage	0.00%
Restricted Stock Units (RSUs) \| Performance Shares \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance shares, target performance percentage	200.00%
Common Stock Equivalents (CSEs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments number of shares unvested (in shares)	110,013	107,338
Grants during period (in shares)	5,852
Base fee percentage	50.00%