Employees
| Concept | As at 2024-09-30 | As at 2024-09-30 | As at 2023-09-30 | As at 2023-09-30 | As at 2022-09-30 | As at 2022-09-30 | As at 2021-09-30 | As at 2021-09-30 | As at 2020-09-30 | As at 2020-09-30 | 
|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||
| Information about reporting company | ||||||||||
| Information about employees of reporting company | ||||||||||
| Number of employees | 
                                                157
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                145
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                165
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                152
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                162
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                148
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                173
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                157
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                159
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                176
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                20
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                20
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                19
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                19
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                18
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                18
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                18
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                25
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                25
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | 
                                                46.7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | 
                                                17
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Months) | — | 
                                                11
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | 
                                                4,936,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |