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 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 | 
                                                561
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                981
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                940
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                178
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                70
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                66
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                157
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                136
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,660
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,482
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                293
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                272
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,499
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,729
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                251
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,110
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                264
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,095
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                290
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                219
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                152
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                211
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | 
                                                586
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                582
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                471
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                399
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                708
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,389
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | — | — | — | — | — | — | — | — | 
                                                37
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average age (Months) | — | — | — | — | — | — | — | — | — | — | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | — | — | — | — | 
                                                12
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Months) | — | — | — | — | — | — | — | — | — | — | 
                                                5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | — | — | — | — | 
                                                7,987,305
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |