Employees
| Concept | As at 2024-04-30 | As at 2024-04-30 | As at 2024-04-30 | As at 2024-04-30 | As at 2023-04-30 | As at 2023-04-30 | As at 2022-04-30 | As at 2022-04-30 | As at 2021-04-30 | As at 2021-04-30 | As at 2020-04-30 | As at 2020-04-30 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||
| Information about reporting company | ||||||||||||
| Information about employees of reporting company | ||||||||||||
| Number of employees | 
                                                258
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                258
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                364
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                364
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                282
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                384
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                291
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                393
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                402
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                310
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                395
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                322
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | 
                                                44.44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | 
                                                17.14
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | 
                                                3,937,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — |