Employees
| Concept | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2024-03-31 | As at 2023-03-31 | As at 2023-03-31 | As at 2022-03-31 | As at 2022-03-31 | As at 2021-03-31 | As at 2021-03-31 | As at 2020-03-31 | As at 2020-03-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | ||||||||||||||||
| Information about reporting company | ||||||||||||||||
| Information about employees of reporting company | ||||||||||||||||
| Number of employees | 
                                                537
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                300
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                278
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                893
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                78
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                93
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                145
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                62
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                920
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                312
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                315
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                946
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                954
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                303
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                301
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                944
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                903
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                109
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                51
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                960
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                26
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                78
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                968
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                104
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                104
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                932
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,082
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                111
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                135
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,101
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | 
                                                41.5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | 
                                                17.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Average annual salary | — | 
                                                5,929,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — |