Employees
| Concept | 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 | As at 2019-09-30 | As at 2019-09-30 | 
|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||
| Information about reporting company | ||||||||||
| Information about employees of reporting company | ||||||||||
| Number of employees | 
                                                1,636
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,264
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,587
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,224
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,547
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,183
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,131
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,483
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,321
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,098
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                734
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                430
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                686
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                413
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                664
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                394
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                392
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                658
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                650
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                394
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average age (Months) | — | 
                                                9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | 
                                                13
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Months) | — | 
                                                11
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | 
                                                7,932,705
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |