Stock-based Compensation (Schedule of SARs Oustanding) (Details) - SARs [Member]	12 Months Ended
Dec. 31, 2017 $ / shares shares
SARs
Balance at December 31, 2016 \| shares	261,206
Exercised \| shares	(26,970)
Forfeited \| shares
Balance at December 31, 2017 \| shares	234,236
Exercisable at December 31, 2017 \| shares	234,236
Weighted Average Exercise Price
Balance at December 31, 2016 \| $ / shares	$ 34.75
Exercised \| $ / shares	33.09
Forfeited \| $ / shares
Balance at December 31, 2017 \| $ / shares	34.97
Exercisable at December 31, 2017 \| $ / shares	$ 34.97

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

+ References

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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-Publisher FASB
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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Number of shares (or other type of equity) forfeited during the period.

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Number of share options (or share units) exercised during the current period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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