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Stock Compensation Plans (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock options outstanding (in shares) | 0 | 0
RSAs |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Awards other than options outstanding (in shares) | 0 | 0
RSUs | Ratably |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Vesting period | 3 years |
RSUs | Cliff | Minimum |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Vesting period | 3 years |
RSUs | Cliff | Maximum |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Vesting period | 5 years |
Performance-Based RSUs |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Awards other than options outstanding (in shares) | 411,290 | 424,299
Total unrecognized compensation cost | $ 26.0 |
Weighted average period to recognize unrecognized compensation cost | 2 years 4 months 13 days |
Performance-Based RSUs | Minimum |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Potential for awards to vest (as a percent) | 0.00% |
Performance-Based RSUs | Maximum |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Potential for awards to vest (as a percent) | 200.00% |
Performance-Based RSUs | Cliff |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Vesting period | 3 years |
Time-Based RSUs |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Awards other than options outstanding (in shares) | 1,214,611 | 1,166,580
Total unrecognized compensation cost | $ 46.8 |
Weighted average period to recognize unrecognized compensation cost | 2 years 5 months 8 days |

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- Definition Unrecognized cost of unvested share-based compensation awards. + 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 (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, 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 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + 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 + Details
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