Employee service share based compensation tax expenses recognized for stock options.

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- Definition

Employee share purchase plan maximum saving by employee.

+ References

No definition available.

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- Definition

Share based compensation arrangement by share based payment award fair value adjustments.

+ References

No definition available.

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- Definition

Share based compensation arrangement by share based payment award number of arrangements.

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No definition available.

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Employee Contribution, Period

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Unrecognized cost of unvested share-based compensation awards.

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-Publisher FASB
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

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

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

A credit or adjustment for government or taxing authority authorized decrease in taxes owed as a result of meeting certain tax policy conditions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

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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- Definition

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.

+ References

No definition available.

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- Definition

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.

+ References

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- Definition

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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

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- Definition

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

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- Definition

Percentage of vesting of share-based compensation awards.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

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- Definition

Number of shares of capital stock issued (purchased by employees) in connection with an employee stock ownership plan.

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Share-Based Payments - Additional Information (Details)		12 Months Ended
Share-Based Payments - Additional Information (Details)	Apr. 05, 2014 GBP (£)	Dec. 31, 2017 USD ($) agreement shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of arrangements under options and equity incentive plans \| agreement		3
Vesting period (in years)		3 years
Compensation cost				$ (6,500,000)
Total tax credit		$ 100,000	$ 500,000	$ 1,500,000
Percentages for vesting		100.00%
Contract period (in years)		10 years
Options exercised \| shares		0	29,222	189,215
Intrinsic value of options		$ 0	$ 600,000	$ 4,300,000
Employee Stock Ownership Plan, shares issued during period (in shares) \| shares		46,866	21,285	59,940
Restricted Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost		$ (9,400,000)	$ (9,800,000)	$ (8,700,000)
Total tax credit		2,300,000	2,400,000	1,800,000
Unrecognized share compensation costs, RSUs		$ 11,000,000
Weighted average period of compensation cost recognition		1 year 7 months 6 days
Compensation cost, non employee directors		$ 1,500,000	1,400,000	1,800,000
Tax charge, non employee directors		0	0	0
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost		(400,000)	(2,200,000)
Unrecognized share compensation costs, RSUs		$ 10,000,000
Weighted average period of compensation cost recognition		1 year 8 months 12 days
Percentages for vesting		33.33%
Phantom Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost		$ (700,000)	(700,000)	(4,300,000)
Unrecognized share compensation costs, RSUs		$ 5,700,000
Weighted average period of compensation cost recognition		1 year 9 months 18 days
Fair value adjustment on compensation cost		$ (1,700,000)	(2,900,000)	(3,200,000)
Tax credit recognized by the company		$ 200,000	(700,000)	(1,200,000)
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)		3 years
Percentages for vesting		200.00%
2013 Share Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant \| shares		2,845,683
2003 Share Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant \| shares		595,683
International Employee Share Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee savings under ESPP		$ 500
Employee contribution period (in years)		2 years
2008 Share Save Scheme
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee savings under ESPP \| £	£ 500
Employee contribution period (in years)		3 years
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost		$ (400,000)	(400,000)	(300,000)
Total tax credit		$ 100,000	100,000
Purchase price percentage of fair market value		85.00%
Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost		$ 0	$ 0	$ 0
Options granted (in shares) \| shares		0	4,447	0
Non-Employee Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentages for vesting		8.33%
Non-Employee Directors \| Restricted Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized share compensation costs, RSUs		$ 200,000
Weighted average period of compensation cost recognition		1 month 6 days