| Summary of Significant Accounting Policies - Retirement benefits (Details) - USD ($) | 12 Months Ended | ||
|---|---|---|---|
| Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | |
| Summary of Significant Accounting Policies | |||
| Pension contributions | $ 3,085,000 | $ 2,628,000 | $ 2,810,000 | 
| X | ||||||||||
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- References No definition available. 
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| X | ||||||||||
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- Definition Amount of cost for defined contribution plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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