Employees
| Concept | As at 2024-12-31 | As at 2024-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2020-12-31 | As at 2020-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||
| Information about reporting company | ||||||||||
| Information about employees of reporting company | ||||||||||
| Number of employees | 
                                                896
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                18,032
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                19,808
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                845
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                20,248
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                827
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                836
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                20,894
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                21,477
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                851
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                49
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                57
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                56
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                49
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                113
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                49
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                57
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                230
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                189
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                57
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                44.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | 
                                                18.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | 
                                                7,217,363
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |