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Employee benefit and stock plans (Tables) | 6 Months Ended
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Jun. 30, 2026
Employee benefit and stock plans |
Schedule of components of net periodic pension benefit | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended June 30,
​ | ​ | Pension Benefits
(Dollars in thousands) | ​ | 2026 | ​ | 2025
Net periodic pension benefit: | ​ ​ ​ | ​ | ​ | ​ ​ ​ | ​ | ​
Interest cost | ​ | $ | 158 | ​ | $ | 165
Expected return on plan assets | ​ |  | (242) | ​ |  | (337)
Amortization of unrecognized net loss | ​ |  | 2 | ​ |  | 35
Net periodic pension benefit | ​ | $ | (82) | ​ | $ | (137)
​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Six Months Ended June 30,
​ | ​ | Pension Benefits
(Dollars in thousands) | ​ | 2026 | ​ | 2025
Net periodic pension benefit: | ​ ​ ​ | ​ | ​ | ​ ​ ​ | ​ | ​
Interest cost | ​ | $ | 316 | ​ | $ | 330
Expected return on plan assets | ​ |  | (484) | ​ |  | (674)
Amortization of unrecognized net loss | ​ |  | 4 | ​ |  | 70
Net periodic pension benefit: | ​ | $ | (164) | ​ | $ | (274)
​ ​

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (q) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (h) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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