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Equity Compensation Plans (Estimated Grant Date Fair Value Per Share of Performance Options Granted) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	$ 8.60	$ 8.25	$ 11.12
Performance Stock Options [Member] | Tranche 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	10.00
Performance Stock Options [Member] | Tranche 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	12.50
Performance Stock Options [Member] | Tranche 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	15.00
Performance Stock Options [Member] | Tranche 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	17.50
Performance Stock Options [Member] | Tranche 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	20.00
Performance Stock Options [Member] | Tranche 6 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	25.00
Performance Stock Options [Member] | Tranche 7 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	30.00
Performance Stock Options [Member] | Tranche 8 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	35.00
Performance Stock Options [Member] | Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Price Target	40.00
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.32
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.30
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.27
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.23
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.19
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 6 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.10
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 7 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	4.01
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 8 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	3.92
Fair Value Of 2012 Grant [Member] | Performance Stock Options [Member] | Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	3.83
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.74
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.73
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 6 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.73
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 7 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.71
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 8 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	14.67
Fair Value Of 2014 Grant [Member] | Performance Stock Options [Member] | Tranche 9 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair Value	$ 14.61

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Share based compensation arrangement by share based payment award options grants in period price target.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ 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 (d)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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