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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2020
Share-based Payment Arrangement, Noncash Expense [Abstract] |
Target grants performance share | Target grants of performance shares outstanding at December 31, 2020, were as follows:
Grant Date | Performance Period | Target Grant of Shares
February 2019 | 2019-2021 | 327,194 |
February 2020 | 2020-2022 | 285,980 |
Schedule of share-based payment award, performance shares, valuation assumptions | Assumptions used for grants applicable to the market condition for certain performance shares issued in 2020, 2019 and 2018 were:
|  |  | 2020 |  |  |  | 2019 |  |  |  | 2018 |
Weighted average grant-date fair value |  |  | $40.75 |  |  |  | $35.07 |  |  |  | $34.55 |
Blended volatility range | 15.30 | % | – | 15.97 | % | 19.50 | % | – | 19.69 | % | 17.87 | % | – | 22.14 | %
Risk-free interest rate range | 1.45 | % | – | 1.62 | % | 2.46 | % | – | 2.55 | % | 1.86 | % | – | 2.46 | %
Weighted average discounted dividends per share |  |  | $2.91 |  |  |  | $2.85 |  |  |  | $2.46 |
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, 2020, was as follows:
| Number of Shares | Weighted Average Grant-Date Fair Value
Nonvested at beginning of period | 573,503 |  | $ | 30.81 |
Granted | 285,980 |  | 36.19 |
Additional performance shares earned | 123,147 |  | 27.48 |
Less: |  |
Vested | 369,456 |  | 29.84 |
Nonvested at end of period | 613,174 |  | $ | 33.24 |

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- Definition Tabular disclosure of the changes in outstanding nonvested performance-based units. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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