| 
       in CHF 1 000  | 
    
       
  | 
    
       31.12.2023  | 
    
       
  | 
    
       %  | 
    
       
  | 
    
       31.12.2022  | 
    
       
  | 
    
       %  | 
  |
| 
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
  
| 
       Assets  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
  
| 
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
  
| 
       Cash and cash equivalents  | 
    
       
  | 
    
       
  | 
    
       67 116  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       96 571  | 
    
       
  | 
    
       
  | 
  
| 
       Marketable securities  | 
    
       
  | 
    
       
  | 
    
       55 000  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       –  | 
    
       
  | 
    
       
  | 
  
| 
       Trade receivables third party  | 
    
       
  | 
    
       
  | 
    
       22 339  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       23 146  | 
    
       
  | 
    
       
  | 
  
| 
       Trade receivables group companies  | 
    
       
  | 
    
       
  | 
    
       30 266  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       42 819  | 
    
       
  | 
    
       
  | 
  
| 
       Other short-term receivables third party  | 
    
       
  | 
    
       
  | 
    
       4 910  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       7 674  | 
    
       
  | 
    
       
  | 
  
| 
       Other short-term receivables group companies  | 
    
       
  | 
    
       
  | 
    
       2 152  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       2 122  | 
    
       
  | 
    
       
  | 
  
| 
       Inventories  | 
    
       
  | 
    
       34 750  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       51 900  | 
    
       
  | 
    
       
  | 
  |
| 
       Accrued income  | 
    
       
  | 
    
       
  | 
    
       3 418  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       2 031  | 
    
       
  | 
    
       
  | 
  
| 
       Current assets  | 
    
       
  | 
    
       
  | 
    
       219 951  | 
    
       
  | 
    
       41.4  | 
    
       
  | 
    
       226 263  | 
    
       
  | 
    
       43.6  | 
  
| 
       Property, plant, equipment and intangible assets  | 
    
       
  | 
    
       105 327  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       103 695  | 
    
       
  | 
    
       
  | 
  |
| 
       Investments in subsidiaries  | 
    
       
  | 
    
       163 670  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       149 161  | 
    
       
  | 
    
       
  | 
  |
| 
       Long-term loans group companies  | 
    
       
  | 
    
       
  | 
    
       42 046  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       39 924  | 
    
       
  | 
    
       
  | 
  
| 
       Non-current assets  | 
    
       
  | 
    
       
  | 
    
       311 043  | 
    
       
  | 
    
       58.6  | 
    
       
  | 
    
       292 780  | 
    
       
  | 
    
       56.4  | 
  
| 
       Assets  | 
    
       
  | 
    
       
  | 
    
       530 994  | 
    
       
  | 
    
       100.0  | 
    
       
  | 
    
       519 043  | 
    
       
  | 
    
       100.0  | 
  
| 
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
  
| 
       Liabilities and equity  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
  
| 
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       
  | 
  
| 
       Trade payables third party  | 
    
       
  | 
    
       
  | 
    
       24 530  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       23 406  | 
    
       
  | 
    
       
  | 
  
| 
       Trade payables group companies  | 
    
       
  | 
    
       
  | 
    
       8 341  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       10 635  | 
    
       
  | 
    
       
  | 
  
| 
       Other short-term liabilities third party  | 
    
       
  | 
    
       
  | 
    
       16 115  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       18 933  | 
    
       
  | 
    
       
  | 
  
| 
       Short-term provisions  | 
    
       
  | 
    
       
  | 
    
       561  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       1 463  | 
    
       
  | 
    
       
  | 
  
| 
       Accrued liabilities  | 
    
       
  | 
    
       
  | 
    
       5 294  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       4 656  | 
    
       
  | 
    
       
  | 
  
| 
       Current liabilities  | 
    
       
  | 
    
       
  | 
    
       54 841  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       59 093  | 
    
       
  | 
    
       
  | 
  
| 
       Long-term provisions  | 
    
       
  | 
    
       
  | 
    
       30 514  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       28 662  | 
    
       
  | 
    
       
  | 
  
| 
       Other long-term liabilities  | 
    
       
  | 
    
       
  | 
    
       2 345  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       2 590  | 
    
       
  | 
    
       
  | 
  
| 
       Non-current liabilities  | 
    
       
  | 
    
       
  | 
    
       32 859  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       31 252  | 
    
       
  | 
    
       
  | 
  
| 
       Liabilities  | 
    
       
  | 
    
       
  | 
    
       87 700  | 
    
       
  | 
    
       16.5  | 
    
       
  | 
    
       90 345  | 
    
       
  | 
    
       17.4  | 
  
| 
       Share capital  | 
    
       
  | 
    
       5 050  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       5 050  | 
    
       
  | 
    
       
  | 
  |
| 
       Legal reserves  | 
    
       
  | 
    
       
  | 
    
       40 271  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       40 271  | 
    
       
  | 
    
       
  | 
  
| 
       General reserves  | 
    
       
  | 
    
       
  | 
    
       90 991  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       90 993  | 
    
       
  | 
    
       
  | 
  
| 
       Retained earnings  | 
    
       
  | 
    
       
  | 
    
       389 366  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       367 620  | 
    
       
  | 
    
       
  | 
  
| 
       Treasury shares  | 
    
       
  | 
    
       (82 384)  | 
    
       
  | 
    
       
  | 
    
       
  | 
    
       (75 236)  | 
    
       
  | 
    
       
  | 
  |
| 
       Equity  | 
    
       
  | 
    
       
  | 
    
       443 294  | 
    
       
  | 
    
       83.5  | 
    
       
  | 
    
       428 698  | 
    
       
  | 
    
       82.6  | 
  
| 
       Liabilities and equity  | 
    
       
  | 
    
       
  | 
    
       530 994  | 
    
       
  | 
    
       100.0  | 
    
       
  | 
    
       519 043  | 
    
       
  | 
    
       100.0  |