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 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 | 
                                                490
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                362
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                6,098
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                221
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                823
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,055
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                165
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                82
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                614
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                860
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                843
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                7,895
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,306
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                813
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,238
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                767
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,334
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                712
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                44
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                39
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,050
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                38
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                71
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,189
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                20
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                2
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,189
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                22
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                108
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                141
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                409
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                193
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                147
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                190
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                139
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                209
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                127
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                41.1
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                11.8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                7,678,370
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |