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Stock Plans (Tables) | 12 Months Ended
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Dec. 31, 2020
Stock Plans |
Share-Based Compensation Activity | A summary of the status of the Company’s restricted stock units as of December 31, 2020 and changes during the year ended December 31, 2020, is presented below:
​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted
​ | ​ | ​ | ​ | Average
​ | ​ | ​ | ​ | Grant-Date
Restricted Stock Units |  | Shares |  | Fair Value
Nonvested shares at January 1, 2020 |  | 349,358 | ​ | $ | 73.47
Granted |  | 162,942 | ​ |  | 84.26
Vested |  | (130,623) | ​ |  | 69.47
Canceled |  | (21,774) | ​ |  | 86.80
Nonvested shares at December 31, 2020 |  | 359,903 | ​ |  | 78.41
​

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- Definition Tabular disclosure of the changes in outstanding nonvested restricted stock 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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