Employees
| Concept | 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 | 
                                                675
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,172
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,262
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                664
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                632
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,280
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,292
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                622
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                612
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                2,453
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                10
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                53
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                79
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                167
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                232
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                164
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average age (Years) | 
                                                40.41
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average length of service (Years) | 
                                                15.83
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Average annual salary | 
                                                5,909,463
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — |