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.

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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-Subparagraph (SAB Topic 14.F)
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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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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.

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- References

No definition available.

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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.

+ References

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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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- 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.

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- Definition

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.

+ References

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-Publisher FASB
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Stock plans (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
Stock plans (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Stock plans (other details)
Number of shares reserved for issuance under the LTIP and STIP	2,753,292		2,753,292
Remaining number of shares reserved for issuance	479,086		479,086
Share compensation expenses	$ 16,040	$ 11,146	$ 25,769	$ 20,637
Options
Stock plans (other details)
Life of options			10 years
Restricted share awards
Stock plans (other details)
Share compensation expenses	7,190	9,745	$ 15,303	18,789
Unrecognized share compensation expenses	33,551		$ 33,551		$ 48,907
Weighted average period of recognizing share based compensation expenses			2 years 1 month 9 days		2 years 3 months 18 days
Restricted share units
Stock plans (other details)
Share compensation expenses	284	327	$ 616	642
Unrecognized share compensation expenses	1,319		$ 1,319		$ 1,909
Weighted average period of recognizing share based compensation expenses			2 years 3 months 10 days		2 years 4 months 17 days
Performance shares
Stock plans (other details)
Share compensation expenses	8,566	$ 1,074	$ 9,850	$ 1,206
Unrecognized share compensation expenses	$ 9,501		$ 9,501		$ 7,813
Weighted average period of recognizing share based compensation expenses			1 year 7 months 2 days		1 year 11 months 4 days
Performance share awards performance period			3 years