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 | 
                                                58
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                374
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                350
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                41
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                202
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                32
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                198
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                190
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                23
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                1.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                62.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                69.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                18.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10.8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2.7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                45.5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | 
                                                2.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | 
                                                19,529,299
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |