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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2017
Share-based Compensation [Abstract] |
Target grants performance share | Target grants of performance shares outstanding at December 31, 2017, were as follows:
Grant Date | Performance Period | Target Grant of Shares |
February 2016 | 2016-2018 | 258,825 |
March 2016 | 2016-2018 | 2,151 |
February 2017 | 2017-2019 | 164,558 |
Schedule of share-based payment award, performance shares, valuation assumptions | Assumptions used for grants of performance shares issued in 2017, 2016 and 2015 were:
|  |  | 2017 |  |  |  | 2016 |  |  |  | 2015 |
Weighted average grant-date fair value |  |  |  | $24.31 |  |  |  |  | $14.60 |  |  |  |  | $18.98 |
Blended volatility range | 22.70 | % | – | 25.56 | % | 29.25 | % | – | 32.51 | % | 22.86 | % | – | 24.61 | %
Risk-free interest rate range | .69 | % | – | 1.61 | % | .47 | % | – | .92 | % | .05 | % | – | 1.07 | %
Weighted average discounted dividends per share |  |  |  | $1.70 |  |  |  |  | $1.56 |  |  |  |  | $1.57 |
Summary of the status of the performance share awards | A summary of the status of the performance share awards for the year ended December 31, 2017, was as follows:
| Number of Shares |  | Weighted Average Grant-Date Fair Value |
Nonvested at beginning of period | 664,188 |  | $ | 21.47 |
Granted | 203,646 |  | 24.31 |
Additional performance shares earned | 81,643 |  | 19.22 |
Less: |  |
Vested | 360,319 |  | 24.88 |
Forfeited | 163,624 |  | 24.46 |
Nonvested at end of period | 425,534 |  | $ | 18.35 |

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- Definition Tabular disclosure of components of a stock option or other award plan under which equity-based compensation is awarded to employees, typically comprised of the amount of unearned compensation (deferred compensation cost), compensation expense, and changes in the quantity and fair value of the shares (or other type of equity) granted, exercised, forfeited, and issued and outstanding pertaining to that plan. Disclosure may also include nature and general terms of such arrangements that existed during the period and potential effects of those arrangements on shareholders, effect of compensation cost arising from equity-based payment arrangements on the income statement, method of estimating the fair value of the goods or services received, or the fair value of the equity instruments granted, during the period, cash flow effects resulting from equity-based payment arrangements and, for registrants that accelerate vesting of out of the money share options, reasons for the decision to accelerate. + 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 1 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 + Details
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- Definition Tabular disclosure of the changes in outstanding nonvested performance-based units. + 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) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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