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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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- 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 + Details
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