| Concept | 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 | 
                                                1,717
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,717
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,208
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,167
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,649
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,608
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,132
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,103
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,585
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,598
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1,087
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | — | — | 
                                                43.4
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | — | — | 
                                                16.0
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Average annual salary | — | — | 
                                                9,852,976
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — |