The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

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- Definition

Weighted average expected volatility rate of share-based compensation awards.

+ References

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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

Expected term of share-based compensation awards, 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 (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: 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.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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Share-Based Payments (Black Scholes Option Pricing Model Assumptions) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield (in percentage)	0.12%		0.11%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period of awards	2 months 12 days	3 months 18 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period of awards	9 years 8 months 12 days	10 years
Weighted-average
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, weighted-average (in percentage)	21.69%		21.55%
Risk-free rate, weighted-average (in percentage)	2.19%		1.82%