| Concept | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | As at 2025-03-31 | 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 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Employees | |||||||||||||||
| Information about reporting company | |||||||||||||||
| Information about employees of reporting company | |||||||||||||||
| Number of employees | 
                                                4,167
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,610
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,258
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10,519
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                13,132
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                31,428
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,258
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,416
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                31,437
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                31,628
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,474
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,633
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                31,963
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                31,933
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,770
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                606
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3,420
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                2,758
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,998
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8,782
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                8,982
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                10,627
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                11,729
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                12,246
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Average age (Years) | — | — | — | — | — | — | 
                                                42.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | — | — | — | — | 
                                                19.8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | — | — | — | — | 
                                                9,732,263
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |