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Retirement Plans and Employee Stock Purchase Plans (Tables) | 12 Months Ended
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Dec. 31, 2023
Retirement Plans and Employee Stock Purchase Plans |
Schedule of purchases made under the 2009 Employee Stock Purchase Plans | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year ended December 31, |
​ | ​ | 2023 | ​ | 2022 | ​ | 2021 |
Number of shares purchased |  | ​ | 117,350 |  | ​ | 105,606 |  | ​ | 63,962 | ​
Average price of shares purchased | ​ | $ | 23.47 | ​ | $ | 26.66 | ​ | $ | 39.70 | ​

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- Definition Tabular disclosure of employee stock purchase plan activity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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