Retirement and Share-based Compensation Plans (Schedule of Stock Options Outstanding, By Exercise Price Range) (Details)	12 Months Ended
Dec. 31, 2017 $ / shares shares
Exercise Price Range I [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	$ 5.07
Exercise price range, upper range limit	$ 8.02
Stock options outstanding and vested, number of awards \| shares	182,500
Stock options outstanding and vested, remaining life (yrs)	1 year 4 months 11 days
Stock options outstanding and vested, weighted-average exercise price per share	$ 6.85
Exercise Price Range II [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	9.27
Exercise price range, upper range limit	$ 11.35
Stock options outstanding and vested, number of awards \| shares	575,055
Stock options outstanding and vested, remaining life (yrs)	1 year 9 months 1 day
Stock options outstanding and vested, weighted-average exercise price per share	$ 10.15
Exercise Price Range III [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	12.04
Exercise price range, upper range limit	$ 24.79
Stock options outstanding and vested, number of awards \| shares	1,222,710
Stock options outstanding and vested, remaining life (yrs)	2 years 6 months 12 days
Stock options outstanding and vested, weighted-average exercise price per share	$ 20.44
Exercise Price Range, All Options [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	5.07
Exercise price range, upper range limit	$ 24.79
Stock options outstanding and vested, number of awards \| shares	1,980,265
Stock options outstanding and vested, remaining life (yrs)	2 years 2 months 13 days
Stock options outstanding and vested, weighted-average exercise price per share	$ 16.20

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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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.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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

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- Definition

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, 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
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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