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Retirement Plans (Tables) | 12 Months Ended
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Dec. 31, 2023
Non-contributory defined benefit pension plan |
Retirement Plans |
Schedule of expenses incurred and charged against operations with regard to all of the company's retirement plans | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31, |
(Dollars in thousands) | ​ | 2023 | ​ | 2022 | ​ | 2021 |
Employee savings plan/ 401(k) | ​ | $ | 16,528 | ​ | $ | 15,357 | ​ | $ | 14,991 | ​
Supplemental executive retirement plan | ​ |  | (3,252) | ​ |  | (1,510) | ​ |  | 3,475 | ​
Split dollar plan | ​ | ​ | (753) | ​ | ​ | (105) | ​ | ​ | (785) | ​
Post-retirement benefits | ​ |  | 312 | ​ |  | (108) | ​ |  | 67 | ​
​ | ​ | $ | 12,835 | ​ | $ | 13,634 | ​ | $ | 17,748 | ​

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- Definition Tabular disclosure of the costs related to the various types of retirement plans including defined benefit pension plan cost, defined contribution plan cost, other postretirement benefit plan cost, and net periodic benefit cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 20 -Topic 715 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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