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
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Section 50
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-Publisher FASB
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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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-Paragraph 2
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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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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
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- Definition

The aggregate cash inflow comprised of the amount received from (a) employees to acquire the entity's shares under incentive awards, including stock option exercises and restricted stock arrangements, and (b) the excess tax benefit arising from such transactions.

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- Definition

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).

+ References

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

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
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- Definition

The performance period, expressed in years, for performance shares awards.

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Stock plans (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Stock plans (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	1,251,411								1,251,411
Share compensation expenses	$ 10,442	$ 10,501	$ 10,727	$ 11,237	$ 10,062	$ 9,983	$ 9,242	$ 9,054	$ 42,907	$ 38,341	$ 33,073
Intrinsic value of options outstanding	831				1,740				831	1,740
Tax benefit from share compensation expenses									1,869	3,436	1,610
Net windfall taxes on vestings and exercises of stock options during the period									$ 1,203	906	3,513
Options [Member]
Stock plans (other details)
Life of options									10 years
Restricted share awards [Member]
Stock plans (other details)
Share compensation expenses									$ 36,887	35,386	31,335
Unrecognized share compensation expenses	58,804				69,143				$ 58,804	$ 69,143
Weighted average period of recognizing share based compensation expenses									2 years 3 months 3 days	2 years 4 months 24 days
Restricted share units [Member]
Stock plans (other details)
Share compensation expenses									$ 1,285	$ 1,160	876
Unrecognized share compensation expenses	2,542				2,790				$ 2,542	$ 2,790
Weighted average period of recognizing share based compensation expenses									2 years 6 months 21 days	2 years 7 months
Performance Shares [Member]
Stock plans (other details)
Share compensation expenses									$ 4,735	$ 1,795	$ 862
Unrecognized share compensation expenses	$ 6,902				$ 4,011				$ 6,902	$ 4,011
Weighted average period of recognizing share based compensation expenses									2 years 21 days	2 years 1 month 6 days
Performance Share Awards Performance Period									3 years