Employees
| Concept | As at 2025-02-28 | As at 2024-02-29 | As at 2023-02-28 | As at 2022-02-28 | As at 2021-02-28 | 
|---|---|---|---|---|---|
| Employees | |||||
| Information about reporting company | |||||
| Information about employees of reporting company | |||||
| Number of employees | 
                                                152
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                162
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                197
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                244
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                274
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                142
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                140
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                123
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                72
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                66
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                41.2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
| Average length of service (Years) | 
                                                18.5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
| Average annual salary | 
                                                4,046,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — |