Shareholders' Equity and Common Stock Equivalents - Outstanding Stock Units and Stock Options under Comprehensive Plan (Details) - shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options	719,015	747,032	669,693
RSUs related to incentive compensation	1,149,679	1,419,268	1,442,325
Total	1,955,274	2,291,860	2,252,661
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock units related to deferred compensation	61,677	74,058	85,200
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock units related to deferred compensation	24,903	51,502	55,443

Deferred compensation arrangement with individual shares outstanding.

No definition available.

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- Definition

Share based compensation arrangement by share based payment awards equity instruments outstanding.

+ References

No definition available.

+ Details

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ 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 (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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.

+ Details

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- Definition

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

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

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